RESUMEN
Poxviruses use virus-encoded multisubunit RNA polymerases (vRNAPs) and RNA-processing factors to generate m7G-capped mRNAs in the host cytoplasm. In the accompanying paper, we report structures of core and complete vRNAP complexes of the prototypic Vaccinia poxvirus (Grimm et al., 2019; in this issue of Cell). Here, we present the cryo-electron microscopy (cryo-EM) structures of Vaccinia vRNAP in the form of a transcribing elongation complex and in the form of a co-transcriptional capping complex that contains the viral capping enzyme (CE). The trifunctional CE forms two mobile modules that bind the polymerase surface around the RNA exit tunnel. RNA extends from the vRNAP active site through this tunnel and into the active site of the CE triphosphatase. Structural comparisons suggest that growing RNA triggers large-scale rearrangements on the surface of the transcription machinery during the transition from transcription initiation to RNA capping and elongation. Our structures unravel the basis for synthesis and co-transcriptional modification of poxvirus RNA.
Asunto(s)
ARN Polimerasas Dirigidas por ADN/química , Metiltransferasas/química , Complejos Multienzimáticos/química , Nucleotidiltransferasas/química , Monoéster Fosfórico Hidrolasas/química , Virus Vaccinia/ultraestructura , Proteínas Virales/química , Microscopía por Crioelectrón , Complejos Multienzimáticos/ultraestructura , ARN Mensajero/química , Imagen Individual de Molécula , Transcripción Genética , Virus Vaccinia/genética , Virus Vaccinia/metabolismoRESUMEN
Poxviruses encode a multisubunit DNA-dependent RNA polymerase (vRNAP) that carries out viral gene expression in the host cytoplasm. We report cryo-EM structures of core and complete vRNAP enzymes from Vaccinia virus at 2.8 Å resolution. The vRNAP core enzyme resembles eukaryotic RNA polymerase II (Pol II) but also reveals many virus-specific features, including the transcription factor Rap94. The complete enzyme additionally contains the transcription factor VETF, the mRNA processing factors VTF/CE and NPH-I, the viral core protein E11, and host tRNAGln. This complex can carry out the entire early transcription cycle. The structures show that Rap94 partially resembles the Pol II initiation factor TFIIB, that the vRNAP subunit Rpo30 resembles the Pol II elongation factor TFIIS, and that NPH-I resembles chromatin remodeling enzymes. Together with the accompanying paper (Hillen et al., 2019), these results provide the basis for unraveling the mechanisms of poxvirus transcription and RNA processing.
Asunto(s)
ARN Polimerasas Dirigidas por ADN/química , Factores de Transcripción/química , Virus Vaccinia/ultraestructura , Proteínas Virales/química , Microscopía por Crioelectrón , Complejos Multienzimáticos/química , Complejos Multienzimáticos/ultraestructura , Imagen Individual de Molécula , Virus Vaccinia/genética , Virus Vaccinia/metabolismoRESUMEN
The MYCN oncoprotein drives the development of numerous neuroendocrine and pediatric tumors. Here we show that MYCN interacts with the nuclear RNA exosome, a 3'-5' exoribonuclease complex, and recruits the exosome to its target genes. In the absence of the exosome, MYCN-directed elongation by RNA polymerase II (RNAPII) is slow and non-productive on a large group of cell-cycle-regulated genes. During the S phase of MYCN-driven tumor cells, the exosome is required to prevent the accumulation of stalled replication forks and of double-strand breaks close to the transcription start sites. Upon depletion of the exosome, activation of ATM causes recruitment of BRCA1, which stabilizes nuclear mRNA decapping complexes, leading to MYCN-dependent transcription termination. Disruption of mRNA decapping in turn activates ATR, indicating transcription-replication conflicts. We propose that exosome recruitment by MYCN maintains productive transcription elongation during S phase and prevents transcription-replication conflicts to maintain the rapid proliferation of neuroendocrine tumor cells.
Asunto(s)
Núcleo Celular/enzimología , Proliferación Celular , Replicación del ADN , Exosomas/enzimología , Proteína Proto-Oncogénica N-Myc/metabolismo , Neuroblastoma/enzimología , ARN Polimerasa II/metabolismo , Transcripción Genética , Animales , Proteínas de la Ataxia Telangiectasia Mutada/genética , Proteínas de la Ataxia Telangiectasia Mutada/metabolismo , Proteína BRCA1/genética , Proteína BRCA1/metabolismo , Línea Celular Tumoral , Núcleo Celular/genética , Roturas del ADN de Doble Cadena , Exorribonucleasas/genética , Exorribonucleasas/metabolismo , Exosomas/genética , Femenino , Regulación Neoplásica de la Expresión Génica , Células HEK293 , Humanos , Masculino , Ratones , Proteína Proto-Oncogénica N-Myc/genética , Células 3T3 NIH , Neuroblastoma/genética , Neuroblastoma/patología , Regiones Promotoras Genéticas , Caperuzas de ARN/genética , Caperuzas de ARN/metabolismo , ARN Polimerasa II/genética , Terminación de la Transcripción GenéticaRESUMEN
Herpesviruses have mastered host cell modulation and immune evasion to augment productive infection, life-long latency and reactivation1,2. A long appreciated, yet undefined relationship exists between the lytic-latent switch and viral non-coding RNAs3,4. Here we identify viral microRNA (miRNA)-mediated inhibition of host miRNA processing as a cellular mechanism that human herpesvirus 6A (HHV-6A) exploits to disrupt mitochondrial architecture, evade intrinsic host defences and drive the switch from latent to lytic virus infection. We demonstrate that virus-encoded miR-aU14 selectively inhibits the processing of multiple miR-30 family members by direct interaction with the respective primary (pri)-miRNA hairpin loops. Subsequent loss of miR-30 and activation of the miR-30-p53-DRP1 axis triggers a profound disruption of mitochondrial architecture. This impairs induction of type I interferons and is necessary for both productive infection and virus reactivation. Ectopic expression of miR-aU14 triggered virus reactivation from latency, identifying viral miR-aU14 as a readily druggable master regulator of the herpesvirus lytic-latent switch. Our results show that miRNA-mediated inhibition of miRNA processing represents a generalized cellular mechanism that can be exploited to selectively target individual members of miRNA families. We anticipate that targeting miR-aU14 will provide new therapeutic options for preventing herpesvirus reactivations in HHV-6-associated disorders.
Asunto(s)
Herpesviridae , MicroARNs , Herpesviridae/genética , Herpesviridae/metabolismo , Humanos , Evasión Inmune , MicroARNs/genética , MicroARNs/metabolismo , Interferencia de ARN , Procesamiento Postranscripcional del ARN , Latencia del Virus/genéticaRESUMEN
The La-related protein 7 (LARP7) forms a complex with the nuclear 7SK RNA to regulate RNA polymerase II transcription. It has been implicated in cancer and the Alazami syndrome, a severe developmental disorder. Here, we report a so far unknown role of this protein in RNA modification. We show that LARP7 physically connects the spliceosomal U6 small nuclear RNA (snRNA) with a distinct subset of box C/D small nucleolar RNAs (snoRNAs) guiding U6 2'-O-methylation. Consistently, these modifications are severely compromised in the absence of LARP7. Although general splicing remains largely unaffected, transcriptome-wide analysis revealed perturbations in alternative splicing in LARP7-depleted cells. Importantly, we identified defects in 2'-O-methylation of the U6 snRNA in Alazami syndrome siblings carrying a LARP7 mutation. Our data identify LARP7 as a bridging factor for snoRNA-guided modification of the U6 snRNA and suggest that alterations in splicing fidelity contribute to the etiology of the Alazami syndrome.
Asunto(s)
Empalme Alternativo , Discapacidades del Desarrollo/metabolismo , ARN Nuclear Pequeño/metabolismo , Ribonucleoproteínas/metabolismo , Empalmosomas/metabolismo , Sitios de Unión , Línea Celular Tumoral , Niño , Preescolar , Secuencia Conservada , Discapacidades del Desarrollo/genética , Femenino , Predisposición Genética a la Enfermedad , Células HEK293 , Humanos , Masculino , Metilación , Persona de Mediana Edad , Mutación , Conformación de Ácido Nucleico , Unión Proteica , Dominios y Motivos de Interacción de Proteínas , ARN Nuclear Pequeño/genética , Ribonucleoproteínas/genética , Empalmosomas/genéticaRESUMEN
U6 snRNA, as an essential component of the catalytic core of the pre-mRNA processing spliceosome, is heavily modified post-transcriptionally, with 2'-O-methylation being most common. The role of these modifications in pre-mRNA splicing as well as their physiological function in mammals have remained largely unclear. Here we report that the La-related protein LARP7 functions as a critical cofactor for 2'-O-methylation of U6 in mouse male germ cells. Mechanistically, LARP7 promotes U6 loading onto box C/D snoRNP, facilitating U6 2'-O-methylation by box C/D snoRNP. Importantly, ablation of LARP7 in the male germline causes defective U6 2'-O-methylation, massive alterations in pre-mRNA splicing, and spermatogenic failure in mice, which can be rescued by ectopic expression of wild-type LARP7 but not an U6-loading-deficient mutant LARP7. Our data uncover a novel role of LARP7 in regulating U6 2'-O-methylation and demonstrate the functional requirement of such modification for splicing fidelity and spermatogenesis in mice.
Asunto(s)
Precursores del ARN/metabolismo , Empalme del ARN , ARN Mensajero/metabolismo , ARN Nuclear Pequeño/metabolismo , Proteínas de Unión al ARN/metabolismo , Espermatogénesis , Espermatozoides/metabolismo , Empalmosomas/metabolismo , Animales , Fertilidad , Regulación del Desarrollo de la Expresión Génica , Células HEK293 , Humanos , Masculino , Metilación , Ratones Endogámicos C57BL , Ratones Noqueados , Precursores del ARN/genética , ARN Mensajero/genética , ARN Nuclear Pequeño/genética , Proteínas de Unión al ARN/genética , Ribonucleoproteínas Nucleolares Pequeñas/genética , Ribonucleoproteínas Nucleolares Pequeñas/metabolismo , Transducción de Señal , Espermatogénesis/genética , Empalmosomas/genéticaRESUMEN
In eukaryotic cells, the process of gene expression is confined to the nucleus and enabled by multisubunit RNA polymerases (RNAPs). Many viruses make use of the host cellular gene expression apparatus during infection, and hence transfer their genome at least transiently to the host nucleus. However, poxviruses have evolved a different strategy to propagate. Their double-stranded DNA genome is transcribed in the host cytoplasm by a virus-encoded RNAP (vRNAP), which is evolutionarily related to eukaryotic RNA polymerase II. In this Review, we highlight recent high-resolution structures of the poxviral transcription apparatus in different phases of action. These structures, along with biochemical data, now allow the definition of a comprehensive model of poxviral gene expression and its regulation.
Asunto(s)
Poxviridae , Núcleo Celular/genética , Citoplasma/genética , ARN Polimerasas Dirigidas por ADN/química , Expresión Génica , Poxviridae/genética , ARN Polimerasa II/genética , Transcripción GenéticaRESUMEN
The year 2022 was marked by the mpox outbreak caused by the human monkeypox virus (MPXV), which is approximately 98% identical to the vaccinia virus (VACV) at the sequence level with regard to the proteins involved in DNA replication. We present the production in the baculovirus-insect cell system of the VACV DNA polymerase holoenzyme, which consists of the E9 polymerase in combination with its co-factor, the A20-D4 heterodimer. This led to the 3.8 Å cryo-electron microscopy (cryo-EM) structure of the DNA-free form of the holoenzyme. The model of the holoenzyme was constructed from high-resolution structures of the components of the complex and the A20 structure predicted by AlphaFold 2. The structures do not change in the context of the holoenzyme compared to the previously determined crystal and NMR structures, but the E9 thumb domain became disordered. The E9-A20-D4 structure shows the same compact arrangement with D4 folded back on E9 as observed for the recently solved MPXV holoenzyme structures in the presence and the absence of bound DNA. A conserved interface between E9 and D4 is formed by a cluster of hydrophobic residues. Small-angle X-ray scattering data show that other, more open conformations of E9-A20-D4 without the E9-D4 contact exist in solution using the flexibility of two hinge regions in A20. Biolayer interferometry (BLI) showed that the E9-D4 interaction is indeed weak and transient in the absence of DNA although it is very important, as it has not been possible to obtain viable viruses carrying mutations of key residues within the E9-D4 interface.
Asunto(s)
Microscopía por Crioelectrón , ADN Polimerasa Dirigida por ADN , Virus Vaccinia , Virus Vaccinia/enzimología , ADN Polimerasa Dirigida por ADN/metabolismo , ADN Polimerasa Dirigida por ADN/química , Holoenzimas/química , Holoenzimas/metabolismo , Proteínas Virales/metabolismo , Proteínas Virales/química , Proteínas Virales/genética , Animales , Humanos , Modelos Moleculares , Conformación Proteica , Cristalografía por Rayos XRESUMEN
Neurogenesis is a finely tuned process, which depends on the balanced execution of expression programs that regulate cellular differentiation and proliferation. Different molecular players ranging from transcription factors to chromatin modulators control these programs. Adding to the complexity, also non-coding (nc)RNAs take part in this process. Here we analyzed the function of the long non-coding (lnc)RNA Malat1 during neural embryonic stem cell (ESC) differentiation. We find that deletion of Malat1 leads to inhibition of proliferation of neural progenitor cells (NPCs). Interestingly, this co-insides with an increase in the expression of miR-26 family members miR-26a and miR-26b in differentiating ESCs. Inactivation of miR-26a/b rescues the proliferative phenotype of Malat1 knockout (KO) cells and leads to accelerated neuronal differentiation of compound Malat1KO/mir-26KO ESCs. Together our work identifies a so far unknown interaction between Malat1 and miR-26 in the regulation of NPC proliferation and neuronal differentiation.
RESUMEN
The P-TEFb complex promotes transcription elongation by releasing paused RNA polymerase II. P-TEFb itself is known to be inactivated through binding to the non-coding RNA 7SK but there is only limited information about mechanisms regulating their association. Here, we show that cells deficient in the RNA-binding protein hnRNP R, a known 7SK interactor, exhibit increased transcription due to phosphorylation of RNA polymerase II. Intriguingly, loss of hnRNP R promotes the release of P-TEFb from 7SK, accompanied by enhanced hnRNP A1 binding to 7SK. Additionally, we found that hnRNP R interacts with BRD4, and that hnRNP R depletion increases BRD4 binding to the P-TEFb component CDK9. Finally, CDK9 is stabilized upon loss of hnRNP R and its association with Cyclin K is enhanced. Together, our results indicate that hnRNP R negatively regulates transcription by modulating the activity and stability of the P-TEFb complex, exemplifying the multimodal regulation of P-TEFb by an RNA-binding protein.
Asunto(s)
Ribonucleoproteínas Nucleares Heterogéneas , Proteínas Nucleares , Factor B de Elongación Transcripcional Positiva , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Células HeLa , Ribonucleoproteínas Nucleares Heterogéneas/genética , Ribonucleoproteínas Nucleares Heterogéneas/metabolismo , Humanos , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Factor B de Elongación Transcripcional Positiva/genética , Factor B de Elongación Transcripcional Positiva/metabolismo , ARN Polimerasa II/genética , ARN Polimerasa II/metabolismo , ARN Largo no Codificante , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Transcripción GenéticaRESUMEN
Macromolecular complexes, rather than individual biopolymers, perform many cellular activities. Faithful assembly of these complexes in vivo is therefore a vital challenge of all cells, and its failure can have fatal consequences. To form functional complexes, cells use elaborate measures to select the "right" components and combine them into working entities. How assembly is achieved at the molecular level is unclear in many cases. Three groups (Jin and colleagues, pp. 2391-2403; Xu and colleagues, pp. 2376-2390; and Tang and colleagues in Cell Research) have now provided insights into how an assembly factor specifically recognizes substrate RNA molecules and enables their usage for assembly of Sm-class uridine-rich small nuclear RNA-protein complexes.
Asunto(s)
Modelos Moleculares , Complejos Multiproteicos/biosíntesis , ARN Nuclear Pequeño/metabolismo , Proteínas del Complejo SMN/química , Proteínas del Complejo SMN/metabolismo , Secuencia de Bases , Complejos Multiproteicos/química , Unión Proteica , Dominios Proteicos , Estructura Terciaria de Proteína , ARN Nuclear Pequeño/química , Alineación de SecuenciaRESUMEN
A deficiency in Survival Motor Neuron (SMN) protein results in motor neuron loss in spinal muscular atrophy (SMA) patients. Human SMN is encoded by SMN1 and SMN2 that differ by a single C6T transition in a splice regulatory region of exon 7. In SMN2, exon 7 is skipped leading to an unstable protein, which cannot compensate for SMN1 loss in SMA patients. The disease severity of human SMA (Types 1-4) depends on the levels of SMN protein, with intermediate levels leading to delayed disease onset and extended life expectancy in Type 2 patients. We used homology directed repair (HDR) to generate a zebrafish mutant with intermediate Smn levels, to mimic intermediate, hSMN2 dependent forms of SMA. In the obtained smnA6Tind27 mutant zebrafish, Smn protein formed oligomers but protein levels dropped significantly at juvenile stages. Motor neurons and neuromuscular junctions (NMJ) also formed normally initially but motor neuron loss and locomotor deficiencies became evident at 21 days. Subsequent muscle wasting and early adult lethality also phenocopied intermediate forms of human SMA. Together, our findings are consistent with the interpretation that Smn is required for neuromuscular maintenance, and establish the smnA6Tind27 zebrafish mutant as a novel model for intermediate types of SMA. As this mutant allows studying the effect of late Smn loss on motor neurons, neuromuscular junctions, and muscle at advanced stages of the disease, it will be a valuable resource for testing new drugs targeted towards treating intermediate forms of SMA.
Asunto(s)
Atrofia Muscular Espinal , Pez Cebra , Animales , Modelos Animales de Enfermedad , Exones/genética , Neuronas Motoras/metabolismo , Atrofia Muscular Espinal/genética , Atrofia Muscular Espinal/metabolismo , Unión Neuromuscular/metabolismo , Proteína 1 para la Supervivencia de la Neurona Motora/genética , Proteína 1 para la Supervivencia de la Neurona Motora/metabolismo , Pez Cebra/genéticaRESUMEN
Repressor element 1-silencing transcription factor (REST) plays a crucial role in the differentiation of neural progenitor cells (NPCs). C-terminal domain small phosphatases (CTDSPs) are REST effector proteins that reduce RNA polymerase II activity on genes required for neurogenesis. miR-26b regulates neurogenesis in zebrafish by targeting ctdsp2 mRNA, but the molecular events triggered by this microRNA (miR) remain unknown. Here, we show in a murine embryonic stem cell differentiation paradigm that inactivation of miR-26 family members disrupts the formation of neurons and astroglia and arrests neurogenesis at the neural progenitor level. Furthermore, we show that miR-26 directly targets Rest, thereby inducing the expression of a large set of REST complex-repressed neuronal genes, including miRs required for induction of the neuronal gene expression program. Our data identify the miR-26 family as the trigger of a self-amplifying system required for neural differentiation that acts upstream of REST-controlled miRs.
Asunto(s)
MicroARNs , Animales , Diferenciación Celular/genética , Ratones , MicroARNs/genética , Neurogénesis/genética , ARN Mensajero/genética , Proteínas Represoras , Factores de Transcripción , Pez Cebra/genéticaRESUMEN
Spliceosomal small nuclear ribonucleoproteins (snRNPs) are essential components of the nuclear pre-mRNA processing machinery. A hallmark of these particles is a ring-shaped core domain generated by the binding of Sm proteins onto snRNA. PRMT5 and SMN complexes mediate the formation of the core domain in vivo. Here, we have elucidated the mechanism of this reaction by both biochemical and structural studies. We show that pICln, a component of the PRMT5 complex, induces the formation of an otherwise unstable higher-order Sm protein unit. In this state, the Sm proteins are kinetically trapped, preventing their association with snRNA. The SMN complex subsequently binds to these Sm protein units, dissociates pICln, and catalyzes ring closure on snRNA. Our data identify pICln as an assembly chaperone and the SMN complex as a catalyst of spliceosomal snRNP formation. The mode of action of this combined chaperone/catalyst system is reminiscent of the mechanism employed by DNA clamp loaders.
Asunto(s)
Proteína Metiltransferasas/química , Ribonucleoproteínas Nucleares Pequeñas/metabolismo , Células HeLa , Humanos , Modelos Biológicos , Chaperonas Moleculares/metabolismo , Proteínas del Tejido Nervioso/metabolismo , Proteína Metiltransferasas/metabolismo , Proteína-Arginina N-Metiltransferasas , ARN/metabolismo , Proteínas de Unión al ARN/metabolismo , Ribonucleoproteínas Nucleares Pequeñas/química , Proteína 1 para la Supervivencia de la Neurona Motora/metabolismoRESUMEN
The macromolecular SMN complex facilitates the formation of Sm-class ribonucleoproteins involved in mRNA processing (UsnRNPs). While biochemical studies have revealed key activities of the SMN complex, its structural investigation is lagging behind. Here we report on the identification and structural determination of the SMN complex from the lower eukaryote Schizosaccharomyces pombe, consisting of SMN, Gemin2, 6, 7, 8 and Sm proteins. The core of the SMN complex is formed by several copies of SMN tethered through its C-terminal alpha-helices arranged with alternating polarity. This creates a central platform onto which Gemin8 binds and recruits Gemins 6 and 7. The N-terminal parts of the SMN molecules extrude via flexible linkers from the core and enable binding of Gemin2 and Sm proteins. Our data identify the SMN complex as a multivalent hub where Sm proteins are collected in its periphery to allow their joining with UsnRNA.
Asunto(s)
Proteínas del Complejo SMN/química , Proteínas de Schizosaccharomyces pombe/química , Proteínas Portadoras/química , Cristalografía por Rayos X , Humanos , Modelos Moleculares , Atrofia Muscular Espinal/genética , Mutación , Proteínas Nucleares/química , Unión Proteica , Proteínas del Complejo SMN/metabolismo , Dispersión del Ángulo Pequeño , Proteínas de Schizosaccharomyces pombe/metabolismo , Homología Estructural de Proteína , Difracción de Rayos XRESUMEN
Malfunction of pre-mRNA processing factors are linked to several human diseases including cancer and neurodegeneration. Here we report the identification of a de novo heterozygous missense mutation in the SNRPE gene (c.65T>C (p.Phe22Ser)) in a patient with non-syndromal primary (congenital) microcephaly and intellectual disability. SNRPE encodes SmE, a basal component of pre-mRNA processing U snRNPs. We show that the microcephaly-linked SmE variant is unable to interact with the SMN complex and as a consequence fails to assemble into U snRNPs. This results in widespread mRNA splicing alterations in fibroblast cells derived from this patient. Similar alterations were observed in HEK293 cells upon SmE depletion that could be rescued by the expression of wild type but not mutant SmE. Importantly, the depletion of SmE in zebrafish causes aberrant mRNA splicing alterations and reduced brain size, reminiscent of the patient microcephaly phenotype. We identify the EMX2 mRNA, which encodes a protein required for proper brain development, as a major mis-spliced down stream target. Together, our study links defects in the SNRPE gene to microcephaly and suggests that alterations of cellular splicing of specific mRNAs such as EMX2 results in the neurological phenotype of the disease.
Asunto(s)
Empalme Alternativo , Proteínas de Homeodominio/genética , Discapacidad Intelectual/genética , Microcefalia/genética , Mutación Missense , Factores de Transcripción/genética , Proteínas Nucleares snRNP/genética , Animales , Línea Celular , Modelos Animales de Enfermedad , Femenino , Células HEK293 , Humanos , Linaje , Empalme del ARN , ARN Mensajero/genética , Ribonucleoproteínas Nucleares Pequeñas/metabolismo , Secuenciación del Exoma , Pez Cebra , Proteínas Nucleares snRNP/química , Proteínas Nucleares snRNP/metabolismoRESUMEN
Interacting bosonic particles in artificial lattices have proven to be a powerful tool for the investigation of exotic phases of matter as well as phenomena resulting from nontrivial topology. Exciton-polaritons, bosonic quasi-particles of light and matter, have been shown to combine the on-chip benefits of optical systems with strong interactions, inherited from their matter character. Technologically significant semiconductor platforms strictly require cryogenic temperatures. In this communication, we demonstrate exciton-polariton lasing for topological defects emerging from the imprinted lattice structure at room temperature. We utilize red fluorescent protein derived from DsRed of Discosoma sea anemones, hosting highly stable Frenkel excitons. Using a patterned mirror cavity, we tune the lattice potential landscape of a linear Su-Schrieffer-Heeger chain to design topological defects at domain boundaries and at the edge. We unequivocally demonstrate polariton lasing from these topological defects. This progress has paved the road to interacting boson many-body physics under ambient conditions.
Asunto(s)
Rayos Láser , Fotones , Semiconductores , TemperaturaRESUMEN
Eukaryotic cells determine the final protein output of their genetic program not only by controlling transcription but also by regulating the localization, translation and turnover rates of their mRNAs. Ultimately, the fate of any given mRNA is determined by the ensemble of all associated RNA-binding proteins (RBPs), non-coding RNAs and metabolites collectively known as the messenger ribonucleoprotein particle (mRNP). Although many mRNA-associated factors have been identified over the past years, little is known about the composition of individual mRNPs and the cooperation of their constituents. In this review we discuss recent progress that has been made on how this 'mRNP code' is established on individual transcripts and how it is interpreted during gene expression in eukaryotic cells.
Asunto(s)
Procesamiento Proteico-Postraduccional/genética , ARN/genética , ARN/metabolismo , Ribonucleoproteínas/genética , Ribonucleoproteínas/metabolismo , Animales , Células Eucariotas/metabolismo , Regulación de la Expresión Génica/genética , HumanosRESUMEN
La and La-related proteins (LARPs) are characterized by a common RNA interaction platform termed the La module. This structural hallmark allows LARPs to pervade various aspects of RNA biology. The metazoan LARP7 protein binds to the 7SK RNA as part of a 7SK small nuclear ribonucleoprotein (7SK snRNP), which inhibits the transcriptional activity of RNA polymerase II (Pol II). Additionally, recent findings revealed unanticipated roles of LARP7 in the assembly of other RNPs, as well as in the modification, processing and cellular transport of RNA molecules. Reduced levels of functional LARP7 have been linked to cancer and Alazami syndrome, two seemingly unrelated human diseases characterized either by hyperproliferation or growth retardation. Here, we review the intricate regulatory networks centered on LARP7 and assess how malfunction of these networks may relate to the etiology of LARP7-linked diseases.
Asunto(s)
Procesamiento Postranscripcional del ARN , ARN no Traducido/genética , ARN no Traducido/metabolismo , Ribonucleoproteínas/metabolismo , Humanos , Conformación de Ácido Nucleico , Estabilidad del ARN , Transporte de ARN , ARN no Traducido/química , Proteínas de Unión al ARN/química , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Ribonucleoproteínas/química , Ribonucleoproteínas/genéticaRESUMEN
Small nuclear ribonucleoproteins (snRNPs) represent key constituents of major and minor spliceosomes. snRNPs contain a common core, composed of seven Sm proteins bound to snRNA, which forms in a step-wise and factor-mediated reaction. The assembly chaperone pICln initially mediates the formation of an otherwise unstable pentameric Sm protein unit. This so-called 6S complex docks subsequently onto the SMN complex, which removes pICln and enables the transfer of pre-assembled Sm proteins onto snRNA. X-ray crystallography and electron microscopy was used to investigate the structural basis of snRNP assembly. The 6S complex structure identifies pICln as an Sm protein mimic, which enables the topological organization of the Sm pentamer in a closed ring. A second structure of 6S bound to the SMN complex components SMN and Gemin2 uncovers a plausible mechanism of pICln elimination and Sm protein activation for snRNA binding. Our studies reveal how assembly factors facilitate formation of RNA-protein complexes in vivo.