RESUMO
Risk management has reduced vulnerability to floods and droughts globally1,2, yet their impacts are still increasing3. An improved understanding of the causes of changing impacts is therefore needed, but has been hampered by a lack of empirical data4,5. On the basis of a global dataset of 45 pairs of events that occurred within the same area, we show that risk management generally reduces the impacts of floods and droughts but faces difficulties in reducing the impacts of unprecedented events of a magnitude not previously experienced. If the second event was much more hazardous than the first, its impact was almost always higher. This is because management was not designed to deal with such extreme events: for example, they exceeded the design levels of levees and reservoirs. In two success stories, the impact of the second, more hazardous, event was lower, as a result of improved risk management governance and high investment in integrated management. The observed difficulty of managing unprecedented events is alarming, given that more extreme hydrological events are projected owing to climate change3.
Assuntos
Secas , Clima Extremo , Inundações , Gestão de Riscos , Mudança Climática/estatística & dados numéricos , Conjuntos de Dados como Assunto , Secas/prevenção & controle , Secas/estatística & dados numéricos , Inundações/prevenção & controle , Inundações/estatística & dados numéricos , Humanos , Hidrologia , Internacionalidade , Gestão de Riscos/métodos , Gestão de Riscos/estatística & dados numéricos , Gestão de Riscos/tendênciasRESUMO
Climate change has led to concerns about increasing river floods resulting from the greater water-holding capacity of a warmer atmosphere1. These concerns are reinforced by evidence of increasing economic losses associated with flooding in many parts of the world, including Europe2. Any changes in river floods would have lasting implications for the design of flood protection measures and flood risk zoning. However, existing studies have been unable to identify a consistent continental-scale climatic-change signal in flood discharge observations in Europe3, because of the limited spatial coverage and number of hydrometric stations. Here we demonstrate clear regional patterns of both increases and decreases in observed river flood discharges in the past five decades in Europe, which are manifestations of a changing climate. Our results-arising from the most complete database of European flooding so far-suggest that: increasing autumn and winter rainfall has resulted in increasing floods in northwestern Europe; decreasing precipitation and increasing evaporation have led to decreasing floods in medium and large catchments in southern Europe; and decreasing snow cover and snowmelt, resulting from warmer temperatures, have led to decreasing floods in eastern Europe. Regional flood discharge trends in Europe range from an increase of about 11 per cent per decade to a decrease of 23 per cent. Notwithstanding the spatial and temporal heterogeneity of the observational record, the flood changes identified here are broadly consistent with climate model projections for the next century4,5, suggesting that climate-driven changes are already happening and supporting calls for the consideration of climate change in flood risk management.
Assuntos
Mudança Climática/estatística & dados numéricos , Inundações/estatística & dados numéricos , Rios , Mudança Climática/história , Europa (Continente) , Inundações/história , Inundações/prevenção & controle , Mapeamento Geográfico , História do Século XX , História do Século XXI , Chuva , Estações do Ano , Fatores de TempoRESUMO
Transcription is punctuated by RNA polymerase (RNAP) pausing. These pauses provide time for diverse regulatory events that can modulate gene expression. Transcription elongation factors dramatically affect RNAP pausing in vitro, but the genome-wide role of such factors on pausing has not been examined. Using native elongating transcript sequencing followed by RNase digestion (RNET-seq), we analyzed RNAP pausing in Bacillus subtilis genome-wide and identified an extensive role of NusG in pausing. This universally conserved transcription elongation factor is known as Spt5 in archaeal and eukaryotic organisms. B. subtilis NusG shifts RNAP to the posttranslocation register and induces pausing at 1,600 sites containing a consensus TTNTTT motif in the nontemplate DNA strand within the paused transcription bubble. The TTNTTT motif is necessary but not sufficient for NusG-dependent pausing. Approximately one-fourth of these pause sites were localized to untranslated regions and could participate in posttranscription initiation control of gene expression as was previously shown for tlrB and the trpEDCFBA operon. Most of the remaining pause sites were identified in protein-coding sequences. NusG-dependent pausing was confirmed for all 10 pause sites that we tested in vitro. Putative pause hairpins were identified for 225 of the 342 strongest NusG-dependent pause sites, and some of these hairpins were shown to function in vitro. NusG-dependent pausing in the ribD riboswitch provides time for cotranscriptional binding of flavin mononucleotide, which decreases the concentration required for termination upstream of the ribD coding sequence. Our phylogenetic analysis implicates NusG-dependent pausing as a widespread mechanism in bacteria.
Assuntos
Bacillus subtilis/genética , Proteínas de Escherichia coli/genética , Regulação Bacteriana da Expressão Gênica/genética , Fatores de Alongamento de Peptídeos/genética , Fatores de Transcrição/genética , Proteínas de Bactérias/metabolismo , RNA Polimerases Dirigidas por DNA/metabolismo , Proteínas de Escherichia coli/metabolismo , Conformação de Ácido Nucleico , Óperon/genética , Fatores de Alongamento de Peptídeos/metabolismo , Fatores de Transcrição/metabolismo , Transcrição Gênica/genética , Fatores de Elongação da Transcrição/genética , Fatores de Elongação da Transcrição/metabolismo , Translocação Genética/genéticaRESUMO
Sensitive and specific serology tests are essential for epidemiological and public health studies of COVID-19 and for vaccine efficacy testing. The presence of antibodies to SARS-CoV-2 surface glycoprotein (Spike) and, specifically, its receptor-binding domain (RBD) correlates with inhibition of SARS-CoV-2 binding to the cellular receptor and viral entry into the cells. Serology tests that detect antibodies targeting RBD have high potential to predict COVID-19 immunity and to accurately determine the extent of the vaccine-induced immune response. Cost-effective methods of expression and purification of Spike and its fragments that preserve antigenic properties are essential for development of such tests. Here we describe a method of production of His6-tagged S319-640 fragment containing RBD in E. coli. It includes expression of the fragment, solubilization of inclusion bodies, and on-the-column refolding. The antigenic properties of the resulting product are similar, but not identical to the RBD-containing fragment expressed in human cells.
Assuntos
COVID-19/virologia , SARS-CoV-2/química , Glicoproteína da Espícula de Coronavírus/química , Sítios de Ligação , Clonagem Molecular , Escherichia coli/química , Escherichia coli/genética , Expressão Gênica , Humanos , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/genética , Fragmentos de Peptídeos/isolamento & purificação , Domínios Proteicos , Redobramento de Proteína , SARS-CoV-2/genética , Solubilidade , Glicoproteína da Espícula de Coronavírus/genética , Glicoproteína da Espícula de Coronavírus/isolamento & purificaçãoRESUMO
UV-induced cyclobutane pyrimidine dimers (CPDs) in the template DNA strand stall transcription elongation by RNA polymerase II (Pol II). If the nucleotide excision repair machinery does not promptly remove the CPDs, stalled Pol II creates a roadblock for DNA replication and subsequent rounds of transcription. Here we present evidence that Pol II has an intrinsic capacity for translesion synthesis (TLS) that enables bypass of the CPD with or without repair. Translesion synthesis depends on the trigger loop and bridge helix, the two flexible regions of the Pol II subunit Rpb1 that participate in substrate binding, catalysis, and translocation. Substitutions in Rpb1 that promote lesion bypass in vitro increase UV resistance in vivo, and substitutions that inhibit lesion bypass decrease cell survival after UV irradiation. Thus, translesion transcription becomes essential for cell survival upon accumulation of the unrepaired CPD lesions in genomic DNA.
Assuntos
Dano ao DNA/efeitos da radiação , Dímeros de Pirimidina/metabolismo , RNA Polimerase II/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/enzimologia , Transcrição Gênica/efeitos da radiação , Raios Ultravioleta/efeitos adversos , Replicação do DNA/genética , Replicação do DNA/efeitos da radiação , DNA Fúngico/biossíntese , DNA Fúngico/genética , Genoma Fúngico/fisiologia , Dímeros de Pirimidina/genética , RNA Polimerase II/genética , Tolerância a Radiação/genética , Tolerância a Radiação/efeitos da radiação , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genética , Transcrição Gênica/genéticaRESUMO
Translocation of RNA polymerase (RNAP) along DNA may be rate-limiting for transcription elongation. The Brownian ratchet model posits that RNAP rapidly translocates back and forth until the post-translocated state is stabilized by NTP binding. An alternative model suggests that RNAP translocation is slow and poorly reversible. To distinguish between these two models, we take advantage of an observation that pyrophosphorolysis rates directly correlate with the abundance of the pre-translocated fraction. Pyrophosphorolysis by RNAP stabilized in the pre-translocated state by bacteriophage HK022 protein Nun was used as a reference point to determine the pre-translocated fraction in the absence of Nun. The stalled RNAP preferentially occupies the post-translocated state. The forward translocation rate depends, among other factors, on melting of the RNA-DNA base pair at the upstream edge of the transcription bubble. DNA-DNA base pairing immediately upstream from the RNA-DNA hybrid stabilizes the post-translocated state. This mechanism is conserved between E. coli RNAP and S. cerevisiae RNA polymerase II and is partially dependent on the lid domain of the catalytic subunit. Thus, the RNA-DNA hybrid and DNA reannealing at the upstream edge of the transcription bubble emerge as targets for regulation of the transcription elongation rate.
Assuntos
RNA Polimerases Dirigidas por DNA/metabolismo , DNA/química , RNA/química , Elongação da Transcrição Genética , Pareamento de Bases , RNA Polimerases Dirigidas por DNA/química , Escherichia coli/enzimologia , Movimento , Domínios Proteicos , RNA Polimerase II/metabolismo , Saccharomyces cerevisiae/enzimologia , Fatores de Transcrição/metabolismo , Proteínas Virais/metabolismoRESUMO
Escherichia coli and yeast DNA-dependent RNA polymerases are shown to mediate efficient nascent transcript stem loop formation-dependent RNA-DNA hybrid realignment. The realignment was discovered on the heteropolymeric sequence T5C5 and yields transcripts lacking a C residue within a corresponding U5C4. The sequence studied is derived from a Roseiflexus insertion sequence (IS) element where the resulting transcriptional slippage is required for transposase synthesis. The stability of the RNA structure, the proximity of the stem loop to the slippage site, the length and composition of the slippage site motif, and the identity of its 3' adjacent nucleotides (nt) are crucial for transcripts lacking a single C. In many respects, the RNA structure requirements for this slippage resemble those for hairpin-dependent transcription termination. In a purified in vitro system, the slippage efficiency ranges from 5% to 75% depending on the concentration ratios of the nucleotides specified by the slippage sequence and the 3' nt context. The only previous proposal of stem loop mediated slippage, which was in Ebola virus expression, was based on incorrect data interpretation. We propose a mechanical slippage model involving the RNAP translocation state as the main motor in slippage directionality and efficiency. It is distinct from previously described models, including the one proposed for paramyxovirus, where following random movement efficiency is mainly dependent on the stability of the new realigned hybrid. In broadening the scope for utilization of transcription slippage for gene expression, the stimulatory structure provides parallels with programmed ribosomal frameshifting at the translation level.
Assuntos
Conformação de Ácido Nucleico , RNA Mensageiro/química , Regiões Terminadoras Genéticas , Transcrição Gênica , Sequência de Aminoácidos , Sequência de Bases , Chloroflexi/genética , RNA Polimerases Dirigidas por DNA/metabolismo , Dados de Sequência Molecular , Motivos de Nucleotídeos/genética , RNA Mensageiro/genética , Saccharomyces cerevisiae/genética , Inversão de SequênciaRESUMO
Recent publications have shown that active RNA polymerase (RNAP) from Mycobacterium tuberculosis (MtbRNAP) can be produced by expressing all four subunits in a single recombinant Escherichia coli strain [1-3]. By reducing the number of plasmids and changing the codon usage of the Mtb genes in the co-expression system published by Banerjee et al. [1], we present a simplified, detailed and reproducible protocol for the purification of recombinant MtbRNAP containing the ω subunit. Moreover, we describe the formation of ternary elongation complexes (TECs) with a short fluorescence-labeled RNA primer and DNA oligonucleotides, suitable for transcription elongation studies. The purification of milligram quantities of the pure and highly active holoenzyme omits ammonium sulfate or polyethylene imine precipitation steps [4] and requires only 5 g of wet cells. Our results indicate that subunit assemblies other than α2ßß'ω·σA can be separated by ion-exchange chromatography on Mono Q column and that assemblies with the wrong RNAP subunit stoichiometry lack transcriptional activity. We show that MtbRNAP TECs can be stalled by NTP substrate deprivation and chased upon the addition of missing NTP(s) without the need of any accessory proteins. Finally, we demonstrate the ability of the purified MtbRNAP to initiate transcription from a promoter and establish that its open promoter complexes are stabilized by the M. tuberculosis protein CarD.
Assuntos
Proteínas de Bactérias , RNA Polimerases Dirigidas por DNA , Mycobacterium tuberculosis/enzimologia , Mycobacterium tuberculosis/genética , Regiões Promotoras Genéticas , Transcrição Gênica , Proteínas de Bactérias/biossíntese , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Proteínas de Bactérias/isolamento & purificação , RNA Polimerases Dirigidas por DNA/biossíntese , RNA Polimerases Dirigidas por DNA/química , RNA Polimerases Dirigidas por DNA/genética , RNA Polimerases Dirigidas por DNA/isolamento & purificação , Escherichia coli/genética , Escherichia coli/metabolismo , Holoenzimas/biossíntese , Holoenzimas/química , Holoenzimas/genética , Holoenzimas/isolamento & purificação , Proteínas Recombinantes/biossíntese , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificaçãoRESUMO
The Nun protein of coliphage HK022 arrests RNA polymerase (RNAP) in vivo and in vitro at pause sites distal to phage λ N-Utilization (nut) site RNA sequences. We tested the activity of Nun on ternary elongation complexes (TECs) assembled with templates lacking the λ nut sequence. We report that Nun stabilizes both translocation states of RNAP by restricting lateral movement of TEC along the DNA register. When Nun stabilized TEC in a pretranslocated register, immediately after NMP incorporation, it prevented binding of the next NTP and stimulated pyrophosphorolysis of the nascent transcript. In contrast, stabilization of TEC by Nun in a posttranslocated register allowed NTP binding and nucleotidyl transfer but inhibited pyrophosphorolysis and the next round of forward translocation. Nun binding to and action on the TEC requires a 9-bp RNA-DNA hybrid. We observed a Nun-dependent toe print upstream to the TEC. In addition, mutations in the RNAP ß' subunit near the upstream end of the transcription bubble suppress Nun binding and arrest. These results suggest that Nun interacts with RNAP near the 5' edge of the RNA-DNA hybrid. By stabilizing translocation states through restriction of TEC lateral mobility, Nun represents a novel class of transcription arrest factors.
Assuntos
RNA Polimerases Dirigidas por DNA/metabolismo , Elongação da Transcrição Genética , Fatores de Transcrição/metabolismo , Proteínas Virais/metabolismo , Bacteriófago lambda/genética , Bacteriófago lambda/metabolismo , DNA Viral/química , DNA Viral/genética , RNA Polimerases Dirigidas por DNA/química , RNA Polimerases Dirigidas por DNA/genética , Difosfatos/metabolismo , Modelos Genéticos , Modelos Moleculares , Mutação , Conformação de Ácido Nucleico , Nucleotídeos/genética , Nucleotídeos/metabolismo , Ligação Proteica , Estrutura Terciária de Proteína , RNA Viral/química , RNA Viral/genética , Moldes Genéticos , Fatores de Transcrição/química , Fatores de Transcrição/genética , Proteínas Virais/química , Proteínas Virais/genéticaRESUMO
We developed a highly sensitive assay to detect transcription errors in vivo. The assay is based on suppression of a missense mutation in the active site tyrosine in the Cre recombinase. Because Cre acts as tetramer, background from translation errors are negligible. Functional Cre resulting from rare transcription errors that restore the tyrosine codon can be detected by Cre-dependent rearrangement of reporter genes. Hence, transient transcription errors are captured as stable genetic changes. We used this Cre-based reporter to screen for mutations of Saccharomyces cerevisiae RPB1 (RPO21) that increase the level of misincorporation during transcription. The mutations are in three domains of Rpb1, the trigger loop, the bridge helix, and in sites involved in binding to TFIIS. Biochemical characterization demonstrates that these variants have elevated misincorporation, and/or ability to extend mispaired bases, or defects in TFIIS mediated editing.
Assuntos
RNA Polimerase II/genética , Proteínas de Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/genética , Transcrição Gênica/genética , Sequência de Aminoácidos , Domínio Catalítico/genética , Códon/genética , Regulação Fúngica da Expressão Gênica/genética , Genes Reporter/genética , Dados de Sequência Molecular , Mutação/genéticaRESUMO
To study fidelity of RNA polymerase II (Pol II), we analyzed properties of the 6-azauracil-sensitive and TFIIS-dependent E1103G mutant of rbp1 (rpo21), the gene encoding the catalytic subunit of Pol II in Saccharomyces cerevisiae. Using an in vivo retrotransposition-based transcription fidelity assay, we observed that rpb1-E1103G causes a 3-fold increase in transcription errors. This mutant showed a 10-fold decrease in fidelity of transcription elongation in vitro. The mutation does not appear to significantly affect translocation state equilibrium of Pol II in a stalled elongation complex. Primarily, it promotes NTP sequestration in the polymerase active center. Furthermore, pre-steady-state analyses revealed that the E1103G mutation shifted the equilibrium between the closed and the open active center conformations toward the closed form. Thus, open conformation of the active center emerges as an intermediate essential for preincorporation fidelity control. Similar mechanisms may control fidelity of DNA-dependent DNA polymerases and RNA-dependent RNA polymerases.
Assuntos
Regulação Fúngica da Expressão Gênica , Mutação/genética , RNA Polimerase II/química , RNA Polimerase II/metabolismo , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/enzimologia , Transcrição Gênica , Sequência de Aminoácidos , Substituição de Aminoácidos , Sítios de Ligação , Domínio Catalítico , Isomerismo , Dados de Sequência Molecular , Nucleotídeos/metabolismo , RNA Polimerase II/genética , Retroelementos/genética , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genética , Alinhamento de Sequência , Especificidade por SubstratoRESUMO
Control over the simultaneous delivery of different functionalities and their synchronized intracellular activation can greatly benefit the fields of RNA and DNA biomedical nanotechnologies and allow for the production of nanoparticles and various switching devices with controllable functions. We present a system of multiple split functionalities embedded in the cognate pairs of RNA-DNA hybrids which are programmed to recognize each other, re-associate and form a DNA duplex while also releasing the split RNA fragments which upon association regain their original functions. Simultaneous activation of three different functionalities (RNAi, Förster resonance energy transfer and RNA aptamer) confirmed by multiple in vitro and cell culture experiments prove the concept. To automate the design process, a novel computational tool that differentiates between the thermodynamic stabilities of RNA-RNA, RNA-DNA and DNA-DNA duplexes was developed. Moreover, here we demonstrate that besides being easily produced by annealing synthetic RNAs and DNAs, the individual hybrids carrying longer RNAs can be produced by RNA polymerase II-dependent transcription of single-stranded DNA templates.
Assuntos
DNA/química , RNA/química , Aptâmeros de Nucleotídeos/química , Linhagem Celular Tumoral , Transferência Ressonante de Energia de Fluorescência , Humanos , Modelos Moleculares , Interferência de RNA , RNA Polimerase II/metabolismo , Termodinâmica , Transcrição GênicaRESUMO
CONSPECTUS: The use of RNAs as scaffolds for biomedical applications has several advantages compared with other existing nanomaterials. These include (i) programmability, (ii) precise control over folding and self-assembly, (iii) natural functionalities as exemplified by ribozymes, riboswitches, RNAi, editing, splicing, and inherent translation and transcription control mechanisms, (iv) biocompatibility, (v) relatively low immune response, and (vi) relatively low cost and ease of production. We have tapped into several of these properties and functionalities to construct RNA-based functional nanoparticles (RNA NPs). In several cases, the structural core and the functional components of the NPs are inherent in the same construct. This permits control over the spatial disposition of the components, intracellular availability, and precise stoichiometry. To enable the generation of RNA NPs, a pipeline is being developed. On one end, it encompasses the rational design and various computational schemes that promote design of the RNA-based nanoconstructs, ultimately producing a set of sequences consisting of RNA or RNA-DNA hybrids, which can assemble into the designed construct. On the other end of the pipeline is an experimental component, which takes the produced sequences and uses them to initialize and characterize their proper assembly and then test the resulting RNA NPs for their function and delivery in cell culture and animal models. An important aspect of this pipeline is the feedback that constantly occurs between the computational and the experimental parts, which synergizes the refinement of both the algorithmic methodologies and the experimental protocols. The utility of this approach is depicted by the several examples described in this Account (nanocubes, nanorings, and RNA-DNA hybrids). Of particular interest, from the computational viewpoint, is that in most cases, first a three-dimensional representation of the assembly is produced, and only then are algorithms applied to generate the sequences that will assemble into the designated three-dimensional construct. This is opposite to the usual practice of predicting RNA structures from a given sequence, that is, the RNA folding problem. To be considered is the generation of sequences that upon assembly have the proper intra- or interstrand interactions (or both). Of particular interest from the experimental point of view is the determination and characterization of the proper thermodynamic, kinetic, functionality, and delivery protocols. Assembly of RNA NPs from individual single-stranded RNAs can be accomplished by one-pot techniques under the proper thermal and buffer conditions or, potentially more interestingly, by the use of various RNA polymerases that can promote the formation of RNA NPs cotransciptionally from specifically designed DNA templates. Also of importance is the delivery of the RNA NPs to the cells of interest in vitro or in vivo. Nonmodified RNAs rapidly degrade in blood serum and have difficulties crossing biological membranes due to their negative charge. These problems can be overcome by using, for example, polycationic lipid-based carriers. Our work involves the use of bolaamphiphiles, which are amphipathic compounds with positively charged hydrophilic head groups at each end connected by a hydrophobic chain. We have correlated results from molecular dynamics computations with various experiments to understand the characteristics of such delivery agents.
Assuntos
Simulação por Computador , Sistemas de Liberação de Medicamentos/métodos , Nanopartículas/química , RNA/química , Algoritmos , Animais , Técnicas de Química Sintética , DNA/química , Interações Hidrofóbicas e Hidrofílicas , Modelos Químicos , Conformação de Ácido Nucleico , RNA/síntese química , Dobramento de RNA , Interferência de RNA , RNA Polimerase II/química , RNA Polimerase II/metabolismo , Riboswitch , TermodinâmicaRESUMO
The fidelity of RNA synthesis depends on both accurate template-mediated nucleotide selection and proper maintenance of register between template and RNA. Loss of register, or transcriptional slippage, is particularly likely on homopolymeric runs in the template. Transcriptional slippage can alter the coding capacity of mRNAs and is used as a regulatory mechanism. Here we describe mutations in the largest subunit of Saccharomyces cerevisiae RNA polymerase II that substantially increase the level of transcriptional slippage. Alleles of RPB1 (RPO21) with elevated slippage rates were identified among 6-azauracil-sensitive mutants and were also isolated using a slippage-dependent reporter gene. Biochemical characterization of polymerase II isolated from these mutants confirms elevated levels of transcriptional slippage.
Assuntos
Regulação Fúngica da Expressão Gênica , Mutação , RNA Polimerase II/genética , RNA Polimerase II/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Alelos , Sequência de Aminoácidos , Sequência de Bases , Domínio Catalítico , Cromossomos/ultraestrutura , Modelos Moleculares , Conformação Molecular , Dados de Sequência Molecular , Oligonucleotídeos/genética , Ligação Proteica , RNA/metabolismo , Transcrição Gênica , beta-Galactosidase/metabolismoRESUMO
The bridge α-helix in the ß' subunit of RNA polymerase (RNAP) borders the active site and may have roles in catalysis and translocation. In Escherichia coli RNAP, a bulky hydrophobic segment near the N-terminal end of the bridge helix is identified (ß' 772-YFI-774; the YFI motif). YFI is located at a distance from the active center and adjacent to a glycine hinge (ß' 778-GARKG-782) involved in dynamic bending of the bridge helix. Remarkably, amino acid substitutions in YFI significantly alter intrinsic termination, pausing, fidelity and translocation of RNAP. F773V RNAP largely ignores the λ tR2 terminator at 200µM NTPs and is strongly reduced in λ tR2 recognition at 1µM NTPs. F773V alters RNAP pausing and backtracking and favors misincorporation. By contrast, the adjacent Y772A substitution increases fidelity and exhibits other transcriptional defects generally opposite to those of F773V. All atom molecular dynamics simulation revealed two separate functional connections emanating from YFI explaining the distinct effects of substitutions: Y772 communicates with the active site through the link domain in the ß subunit, whereas F773 communicates through the fork domain in the ß subunit. I774 interacts with the F-loop, which also contacts the glycine hinge of the bridge helix. These results identified negative and positive circuits coupled at YFI and employed for regulation of catalysis, elongation, termination and translocation.
Assuntos
Motivos de Aminoácidos , Catálise , RNA Polimerases Dirigidas por DNA/química , Escherichia coli/enzimologia , Sequência de Aminoácidos , Sítios de Ligação , Domínio Catalítico , RNA Polimerases Dirigidas por DNA/metabolismo , Cinética , Simulação de Dinâmica Molecular , Dados de Sequência Molecular , Mutagênese , Conformação Proteica , Estrutura Secundária de ProteínaRESUMO
Ribonucleoside analogues have potential utility as anti-viral, -parasitic, -bacterial and -cancer agents. However, their clinical applications have been limited by off target effects. Development of antiviral ribonucleosides for treatment of hepatitis C virus (HCV) infection has been hampered by appearance of toxicity during clinical trials that evaded detection during preclinical studies. It is well established that the human mitochondrial DNA polymerase is an off target for deoxyribonucleoside reverse transcriptase inhibitors. Here we test the hypothesis that triphosphorylated metabolites of therapeutic ribonucleoside analogues are substrates for cellular RNA polymerases. We have used ribonucleoside analogues with activity against HCV as model compounds for therapeutic ribonucleosides. We have included ribonucleoside analogues containing 2'-C-methyl, 4'-methyl and 4'-azido substituents that are non-obligate chain terminators of the HCV RNA polymerase. We show that all of the anti-HCV ribonucleoside analogues are substrates for human mitochondrial RNA polymerase (POLRMT) and eukaryotic core RNA polymerase II (Pol II) in vitro. Unexpectedly, analogues containing 2'-C-methyl, 4'-methyl and 4'-azido substituents were inhibitors of POLRMT and Pol II. Importantly, the proofreading activity of TFIIS was capable of excising these analogues from Pol II transcripts. Evaluation of transcription in cells confirmed sensitivity of POLRMT to antiviral ribonucleosides, while Pol II remained predominantly refractory. We introduce a parameter termed the mitovir (mitochondrial dysfunction caused by antiviral ribonucleoside) score that can be readily obtained during preclinical studies that quantifies the mitochondrial toxicity potential of compounds. We suggest the possibility that patients exhibiting adverse effects during clinical trials may be more susceptible to damage by nucleoside analogs because of defects in mitochondrial or nuclear transcription. The paradigm reported here should facilitate development of ribonucleosides with a lower potential for toxicity.
Assuntos
Antivirais/farmacologia , Núcleo Celular/metabolismo , RNA Polimerases Dirigidas por DNA/metabolismo , Hepacivirus/metabolismo , Mitocôndrias/metabolismo , RNA Polimerase II/metabolismo , Ribonucleosídeos/farmacologia , Transcrição Gênica/efeitos dos fármacos , Animais , Antivirais/efeitos adversos , Bovinos , Linhagem Celular , Hepatite C/tratamento farmacológico , Hepatite C/enzimologia , RNA Viral/biossíntese , Ribonucleosídeos/efeitos adversosRESUMO
We report a generalized methodology for the one-pot production of chemically modified functional RNA nanoparticles during in vitro transcription with T7 RNA polymerase. The efficiency of incorporation of 2'-fluoro-dNTP in the transcripts by the wild type T7 RNA polymerase dramatically increases in the presence of manganese ions, resulting in a high-yield production of chemically modified RNA nanoparticles functionalized with siRNAs that are resistant to nucleases from human blood serum. Moreover, the unpurified transcription mixture can be used for functional ex vivo pilot experiments.
Assuntos
Nanopartículas/química , RNA Interferente Pequeno/química , RNA Interferente Pequeno/genética , RNA/química , Linhagem Celular Tumoral , RNA Polimerases Dirigidas por DNA/metabolismo , Humanos , Nanopartículas/administração & dosagem , Nanotecnologia , RNA/genética , RNA/metabolismo , RNA Interferente Pequeno/metabolismo , Transcrição Gênica , Proteínas Virais/metabolismoRESUMO
Fork loop 2 is a small semiconservative segment of the larger fork domain in the second largest Rpb2 subunit of RNA polymerase II (Pol II). This flexible loop, juxtaposed at the leading edge of transcription bubble, has been proposed to participate in DNA strand separation, translocation along DNA, and NTP loading to Pol II during elongation. Here we show that the Rpb2 mutant carrying a deletion of the flexible part of the loop is not lethal in yeast. The mutation exhibits no defects in DNA melting and translocation in vitro but confers a moderate decrease of the catalytic activity of the enzyme caused by the impaired sequestration of the NTP substrate in the active center prior to catalysis. In the structural model of the Pol II elongation complex, fork loop 2 directly interacts with an unpaired DNA residue in the non-template DNA strand one nucleotide ahead from the active center (the i+2 position). We showed that elimination of this putative interaction by replacement of the i+2 residue with an abasic site inhibits Pol II activity to the same degree as the deletion of fork loop 2. This replacement has no detectable effect on the activity of the mutant enzyme. We provide direct evidence that interaction of fork loop 2 with the non-template DNA strand facilitates NTP sequestration through interaction with the adjacent segment of the fork domain involved in the active center of Pol II.
Assuntos
RNA Polimerase II/química , Thermus thermophilus/enzimologia , Transcrição Gênica , Sequência de Aminoácidos , Animais , Catálise , Domínio Catalítico , Bovinos , DNA/metabolismo , Exodesoxirribonucleases/química , Modelos Moleculares , Dados de Sequência Molecular , Mutação , Permanganato de Potássio/química , Ligação Proteica , RNA Polimerase II/metabolismo , Saccharomyces cerevisiae/metabolismoRESUMO
Sequence-specific pausing of multisubunit RNA polymerases (RNAPs) represents a rate-limiting step during transcription elongation. Pausing occurs on average every 100 bases of DNA. Several models have been proposed to explain pausing, including backtracking of the ternary elongation complex, delay of translocation of the enzyme along DNA, or a conformational change in the active site preventing formation of the phosphodiester bond. Here, we performed biochemical characterization of previously-reported pauses of Escherichia coli RNAP and found that they are not associated with backtracking or a translocation delay. Instead, the paused complex contains the 3' end of the transcript in the active center and is capable of binding the next cognate NTP. However, bond formation occurs much slower in the paused complex compared with its fully-active counterpart. The pausing is dramatically decreased by a substitution of the base encoding the next incoming NTP and the base encoding the 3' end of the nascent RNA, suggesting that (mis)-alignment of the 3' end of the RNA and the incoming NTP in the active site is crucial for pausing. These pause sites are conserved between E. coli and Thermus thermophilus RNAPs, but are not recognized by Saccharomyces cerevisiae RNAP II, indicating that prokaryotic RNAPs might be more sensitive to the changes in the alignment of the nascent transcript and the substrate NTP in the active site.
Assuntos
RNA Polimerases Dirigidas por DNA/metabolismo , DNA/metabolismo , Escherichia coli/enzimologia , RNA Mensageiro/biossíntese , Transcrição Gênica , Bacteriófago T7/genética , Sequência de Bases , Domínio Catalítico , Sequência Conservada , DNA/química , RNA Polimerases Dirigidas por DNA/química , Escherichia coli/genética , Nucleotídeos/química , Nucleotídeos/metabolismo , Saccharomyces cerevisiae/enzimologia , Saccharomyces cerevisiae/genéticaRESUMO
Vaccines against the severe acute respiratory syndrome coronavirus 2, which have been in urgent need and development since the beginning of 2020, are aimed to induce a prominent immune system response capable of recognizing and fighting future infection. Here we analyzed the levels of IgG antibodies against the receptor-binding domain (RBD) of the viral spike protein after the administration of three types of popular vaccines, BNT162b2, mRNA-1273, or Sputnik V, using the same ELISA assay to compare their effects. An efficient immune response was observed in the majority of cases. The obtained ranges of signal values were wide, presumably reflecting specific features of the immune system of individuals. At the same time, these ranges were comparable among the three studied vaccines. The anti-RBD IgG levels after vaccination were also similar to those in the patients with moderate/severe course of the COVID-19, and significantly higher than in the individuals with asymptomatic or light symptomatic courses of the disease. No significant correlation was observed between the levels of anti-RBD IgG and sex or age of the vaccinated individuals. The signals measured at different time points for several individuals after full Sputnik V vaccination did not have a significant tendency to lower within many weeks. The rate of neutralization of the interaction of the RBD with the ACE2 receptor after vaccination with Sputnik V was on average slightly higher than in patients with a moderate/severe course of COVID-19. The importance of the second dose administration of the two-dose Sputnik V vaccine was confirmed: while several individuals had not developed detectable levels of the anti-RBD IgG antibodies after the first dose of Sputnik V, after the second dose the antibody signal became positive for all tested individuals and raised on average 5.4 fold. Finally, we showed that people previously infected with SARS-CoV-2 developed high levels of antibodies, efficiently neutralizing interaction of RBD with ACE2 after the first dose of Sputnik V, with almost no change after the second dose.