The immunostimulatory RNA RN7SL1 enables CAR-T cells to enhance autonomous and endogenous immune function.

Poor tumor infiltration, development of exhaustion, and antigen insufficiency are common mechanisms that limit chimeric antigen receptor (CAR)-T cell efficacy. Delivery of pattern recognition receptor agonists is one strategy to improve immune function; however, targeting these agonists to immune cells is challenging, and off-target signaling in cancer cells can be detrimental. Here, we engineer CAR-T cells to deliver RN7SL1, an endogenous RNA that activates RIG-I/MDA5 signaling. RN7SL1 promotes expansion and effector-memory differentiation of CAR-T cells. Moreover, RN7SL1 is deployed in extracellular vesicles and selectively transferred to immune cells. Unlike other RNA agonists, transferred RN7SL1 restricts myeloid-derived suppressor cell (MDSC) development, decreases TGFB in myeloid cells, and fosters dendritic cell (DC) subsets with costimulatory features. Consequently, endogenous effector-memory and tumor-specific T cells also expand, allowing rejection of solid tumors with CAR antigen loss. Supported by improved endogenous immunity, CAR-T cells can now co-deploy peptide antigens with RN7SL1 to enhance efficacy, even when heterogenous CAR antigen tumors lack adequate neoantigens.

RN7SL1 may be translated under oncogenic conditions.

RN7SL1 (RNA component of signal recognition particle 7SL1), a component of the signal recognition particle, is a non-coding RNA possessing a small ORF (smORF). However, whether it is translated into peptides is unknown. Here, we generated the RN7SL1-Green Fluorescent Protein (GFP) gene, in which the smORF of RN7SL1 was replaced by GFP, introduced it into 293T cells, and observed cells emitting GFP fluorescence. Furthermore, RNA-seq of GFP-positive cells revealed that they were in an oncogenic state, suggesting that RN7SL1 smORF may be translated under special conditions.

Profiling of long non-coding RNAs in hippocampal-entorhinal system subfields: impact of RN7SL1 on neuroimmune response modulation in Alzheimer's disease.

Alzheimer's disease (AD) is recognized as the predominant cause of dementia, and neuroimmune processes play a pivotal role in its pathological progression. The involvement of long non-coding RNAs (lncRNAs) in AD has attracted widespread attention. Herein, transcriptomic analysis of 262 unique samples extracted from five hippocampal-entorhinal system subfields of individuals with AD pathology and without AD pathology revealed distinctive lncRNA expression profiles. Through differential expression and coexpression analyses, we identified 16 pivotal lncRNAs. Notably, RN7SL1 knockdown significantly modulated microglial responses upon oligomeric amyloid-ß stimulation, resulting in a considerable decrease in proinflammatory cytokine production and subsequent neuronal damage. These findings highlight RN7SL1 as an essential neuroimmune-related lncRNA that could serve as a prospective target for AD diagnosis and treatment.

Correlated sequence signatures are present within the genomic 5'UTR RNA and NSP1 protein in coronaviruses.

The 5'UTR part of coronavirus genomes plays key roles in the viral replication cycle and translation of viral mRNAs. The first 75-80 nt, also called the leader sequence, are identical for genomic mRNA and subgenomic mRNAs. Recently, it was shown that cooperative actions of a 5'UTR segment and the nonstructural protein NSP1 are essential for both the inhibition of host mRNAs and for specific translation of viral mRNAs. Here, sequence analyses of both the 5'UTR RNA segment and the NSP1 protein have been done for several coronaviruses, with special attention to the betacoronaviruses. The conclusions are: (i) precise specific molecular signatures can be found in both the RNA and the NSP1 protein; (ii) both types of signatures correlate between each other. Indeed, definite sequence motifs in the RNA correlate with sequence motifs in the protein, indicating a coevolution between the 5'UTR and NSP1 in betacoronaviruses. Experimental mutational data on 5'UTR and NSP1 from SARS-CoV-2 using cell-free translation extracts support these conclusions and show that some conserved key residues in the amino-terminal half of the NSP1 protein are essential for evasion to the inhibitory effect of NSP1 on translation.

The viral protein NSP1 acts as a ribosome gatekeeper for shutting down host translation and fostering SARS-CoV-2 translation.

SARS-CoV-2 coronavirus is responsible for Covid-19 pandemic. In the early phase of infection, the single-strand positive RNA genome is translated into non-structural proteins (NSP). One of the first proteins produced during viral infection, NSP1, binds to the host ribosome and blocks the mRNA entry channel. This triggers translation inhibition of cellular translation. In spite of the presence of NSP1 on the ribosome, viral translation proceeds however. The molecular mechanism of the so-called viral evasion to NSP1 inhibition remains elusive. Here, we confirm that viral translation is maintained in the presence of NSP1. The evasion to NSP1-inhibition is mediated by the cis-acting RNA hairpin SL1 in the 5'UTR of SARS-CoV-2. NSP1-evasion can be transferred on a reporter transcript by SL1 transplantation. The apical part of SL1 is only required for viral translation. We show that NSP1 remains bound on the ribosome during viral translation. We suggest that the interaction between NSP1 and SL1 frees the mRNA accommodation channel while maintaining NSP1 bound to the ribosome. Thus, NSP1 acts as a ribosome gatekeeper, shutting down host translation or fostering SARS-CoV-2 translation depending on the presence of the SL1 5'UTR hairpin. SL1 is also present and necessary for translation of sub-genomic RNAs in the late phase of the infectious program. Consequently, therapeutic strategies targeting SL1 should affect viral translation at early and late stages of infection. Therefore, SL1 might be seen as a genuine 'Achille heel' of the virus.

Mycobacterium tuberculosis (Mtb) lipid mediated lysosomal rewiring in infected macrophages modulates intracellular Mtb trafficking and survival.

Intracellular pathogens commonly manipulate the host lysosomal system for their survival. However, whether this pathogen-induced alteration affects the organization and functioning of the lysosomal system itself is not known. Here, using in vitro and in vivo infections and quantitative image analysis, we show that the lysosomal content and activity are globally elevated in Mycobacterium tuberculosis (Mtb)-infected macrophages. We observed that this enhanced lysosomal state is sustained over time and defines an adaptive homeostasis in the infected macrophage. Lysosomal alterations are caused by mycobacterial surface components, notably the cell wall-associated lipid sulfolipid-1 (SL-1), which functions through the mTOR complex 1 (mTORC1)-transcription factor EB (TFEB) axis in the host cells. An Mtb mutant lacking SL-1, MtbΔpks2, shows attenuated lysosomal rewiring compared with the WT Mtb in both in vitro and in vivo infections. Exposing macrophages to purified SL-1 enhanced the trafficking of phagocytic cargo to lysosomes. Correspondingly, MtbΔpks2 exhibited a further reduction in lysosomal delivery compared with the WT. Reduced trafficking of this mutant Mtb strain to lysosomes correlated with enhanced intracellular bacterial survival. Our results reveal that global alteration of the host lysosomal system is a defining feature of Mtb-infected macrophages and suggest that this altered lysosomal state protects host cell integrity and contributes to the containment of the pathogen.

Generation of Liposomes to Study the Effect of Mycobacterium Tuberculosis Lipids on HIV-1 cis- and trans-Infections.

Tuberculosis (TB) is the leading cause of death among HIV-1-infected individuals and Mycobacterium tuberculosis (Mtb) co-infection is an early precipitate to AIDS. We aimed to determine whether Mtb strains differentially modulate cellular susceptibility to HIV-1 infection (cis- and trans-infection), via surface receptor interaction by their cell envelope lipids. Total lipids from pathogenic (lineage 4 Mtb H37Rv, CDC1551 and lineage 2 Mtb HN878, EU127) and non-pathogenic (Mycobacterium bovis BCG and Mycobacterium smegmatis) Mycobacterium strains were integrated into liposomes mimicking the lipid distribution and antigen accessibility of the mycobacterial cell wall. The resulting liposomes were tested for modulating in vitro HIV-1 cis- and trans-infection of TZM-bl cells using single-cycle infectious virus particles. Mtb glycolipids did not affect HIV-1 direct infection however, trans-infection of both R5 and X4 tropic HIV-1 strains were impaired in the presence of glycolipids from M. bovis, Mtb H37Rv and Mtb EU127 strains when using Raji-DC-SIGN cells or immature and mature dendritic cells (DCs) to capture virus. SL1, PDIM and TDM lipids were identified to be involved in DC-SIGN recognition and impairment of HIV-1 trans-infection. These findings indicate that variant strains of Mtb have differential effect on HIV-1 trans-infection with the potential to influence HIV-1 disease course in co-infected individuals.

Targeting c-met receptor tyrosine kinase by the DNA aptamer SL1 as a potential novel therapeutic option for myeloma.

Hepatocyte growth factor (HGF)/c-met pathway activation has been implicated in the pathogenesis of multiple myeloma (MM), and blocking this pathway has been considered a rational therapeutic strategy for treating MM. Aptamers are single-stranded nucleic acid molecules that fold into complex 3D structures and bind to a variety of targets. Recently, it was reported that DNA aptamer SL1 exhibited high specificity and affinity for c-met and inhibited HGF/c-met signaling in SNU-5 cells. However, as the first c-met-targeted DNA aptamer to be identified, application of SL1 to myeloma treatment requires further investigation. Here, we explore the potential application of SL1 in MM. Our results indicated that c-met expression is gradually increased in MM patients and contributes to poor outcomes. SL1 selectively bound to c-met-positive MM cells but not to normal B cells and suppressed the growth, migration and adhesion of MM cells in vitro in a co-culture model performed with HS5 cells, wherein SL1 inhibited HGF-induced activation of c-met signaling. In vivo and ex vivo fluorescence imaging showed that SL1 accumulated in the c-met positive tumour areas. In addition, SL1 was active against CD138+ primary MM cells and displayed a synergistic inhibition effect with bortezomib. Collectively, our data suggested that SL1 could be beneficial as a c-met targeted antagonist in MM.

Cytotoxicity of chemical constituents from Torricellia tiliifolia DC. on Spodoptera litura (SL-1) cells.

In this study, we evaluated cytotoxicity of chemicals isolated from Torricellia tiliifolia DC. on Spodoptera litura (SL-1) cell line. Among the isolated compounds, 4-hydroxy-3-methoxycinnamaldehyde, 3,5-dimethoxy-4-hydroxycinnamaldehyde, and syringaresinol inhibited SL-1 cell survival in both dose- and time-dependent manners. Meanwhile, the in vivo insecticidal activity test revealed that 4-hydroxy-3-methoxycinnamaldehyde and 3,5-dimethoxy-4-hydroxycinnamaldehyde showed obvious insecticidal activities. These two compounds exhibited toxicity to SL-1 cells by inducing cellular morphological changes including shape change, cell shrinkage, vacuolation, cell membrane blebbing and chromatin condensation and apoptosis. 4-hydroxy-3-methoxycinnamaldehyde and 3,5-dimethoxy-4-hydroxycinnamaldehyde showed the most effect on mitochondrial membrane depolarization at 24h and 72h respectively and induced the apoptosis at a late time point 72h. Our results suggest that 4-hydroxy-3-methoxycinnamaldehyde and 3,5-dimethoxy-4-hydroxycinnamaldehyde inhibit SL-1 survival by inducing apoptosis.

The sL1CAM in sera of patients with endometrial and ovarian cancers.

PURPOSE: L1CAM is a cell adhesion molecule suspected to play an important role in carcinogenesis. The objective of the study was to evaluate the level of soluble L1CAM in the sera of patients with endometrial and ovarian carcinomas and verify the feasibility of the sL1CAM as a marker of these carcinomas. METHODS: 35 endometrial and 18 ovarian cancer patients were enrolled in the study. 43 patients with benign gynecological conditions constituted a control group. The sL1CAM serum level was measured with ELISA test in each patient and it was referred to the data from the surgical staging of the cancers. RESULTS: The sL1CAM serum level was significantly lower in patients with endometrial cancer than in healthy women and slightly lower in the ovarian cancer group than in the control group. In the endometrial cancer group there was no correlation between sL1CAM concentration and cancer histopathology, stage or grade. sL1CAM concentration positively correlated with ovarian cancer stage and (not significantly) with grade. CONCLUSIONS: Despite the increasing data about the possible role of L1CAM as a strong prognostic factor of poor outcome in many cancers, we did not find evidence supporting the use of sL1CAM as a marker of endometrial or ovarian cancers.

Reconstitution of human rRNA gene transcription in mouse cells by a complete SL1 complex.

An important characteristic of the transcription of a ribosomal RNA gene (rDNA) mediated by DNA-dependent RNA polymerase (Pol) I is its stringent species specificity. SL1/TIF-IB is a key complex for species specificity, but its functional complex has not been reconstituted. Here, we established a novel and highly sensitive monitoring system for Pol I transcription to reconstitute the SL1 activity in which a transcript harboring a reporter gene synthesized by Pol I is amplified and converted into translatable mRNA by the influenza virus RNA-dependent RNA polymerase. Using this monitoring system, we reconstituted Pol I transcription from the human rDNA promoter in mouse cells by expressing four human TATA-binding protein (TBP)-associated factors (TAFIs) in the SL1 complex. The reconstituted SL1 also re-activated human rDNA transcription in mouse A9 cells carrying an inactive human chromosome 21 that contains the rDNA cluster. Chimeric SL1 complexes containing human and mouse TAFIs could be formed, but these complexes were inactive for human rDNA transcription. We conclude that four human TAFIs are necessary and sufficient to overcome the barrier of species specificity for human rDNA transcription in mouse cells.

The cytotoxicology of momordicins I and II on Spodoptera litura cultured cell line SL-1.

Momordicin I and II are secondary metabolites from bitter melon (Momordica charantia L.) that are toxic to the Spodoptera litura ovary cell line (SL-1 cell). Both momordicin I and II significantly inhibited SL-1 cells proliferation. IC50 values after 24 h were 8.35 and 82.31 µg/mL, 6.11 and 77.49 µg/mL for 36 h, 4.93 and 49.42 µg/mL for 48 h for cells treated by momordicin I and II, respectively. IC50 values of the azadirachtin A control were 149.63, 54.54 and 23.66 µg/mL at 24, 36 and 48 h respectively, indicating that the cytotoxicity of momordicin I was significantly higher than that of momordicin II and azadirachtin A. Using inverted phase contrast microscopy we found that after 24 h exposure to momordicin I and II, cell shapes changed to circular, swelling increased, adherence ability declined and the cellular membrane bubbled. After 48 h exposure to momordicin I, most cells were suspended and dead; vacuole deformation and cytoplasm leakage indicated that momordicin I was more toxic to the cytoskeleton than momordicin II. Cells treated with momordicin I and II inhibited glucose absorption by 23.04 and 13.38% after 48 h and 47.60 and 20.92% after 60 h. Flow cytometry analysis suggested that SL-1 cells treated with momordicin I and II dramatically accumulated during the G2/M phase of the cell cycle, and total cell protein content increased by 56.93 and 35.81% respectively after 48 h treatment. Following treatment with momordicin I and II the karyotheca dissolved, the chromatin condensed abnormally and the nucleoli were damaged, migrated, or disappeared. The PI fluorescent value by FCM showed that the relative fluorescent intensity of SL-1 cells induced by momordicin I and II increased to 521.45 and 370.17, higher than 135.04 induced by control group treatment for 48 h. This indicated significant damage to the cytomembrane. Overall, the results demonstrate that suppression of cytoskeletal function, interference of mitotic figures and destruction of nuclear structure are effects of momordicin I and II exposure. These effects play major roles in momordicin I and II inhibition of SL-1 cells growth. The mode of action by which momordicins inhibit insect cell growth and development may be useful in the development of novel pest control formulations containing cucurbitane-type triterpene glycosides.

Hypoxia inducible NOD2 interacts with 3-O-sulfogalactoceramide and regulates vesicular homeostasis.

BACKGROUND: Oxygen sensing in mammalian cells is a conserved signaling pathway regulated by hypoxia inducible factor type 1 (HIF-1). Inadequate oxygen supply (hypoxia) is common to many pathological disorders where autophagy plays an import role. The aim of this study was the identification and characterization of novel HIF-1 target genes that promote autophagy during hypoxia. METHODS: Whole genome Chromatin Immune Precipitation from hypoxic HeLa cells was used to identify novel HIF-1 target genes. Hypoxia induced expression and transcription regulation was studied in wild type and HIF-deficient cells. siRNA silencing of candidate genes was used to establish their role during autophagy. Recombinant protein was used for screening immobilized glycosylated lipids to identify potential ligands. RESULTS: We identified the Nucleotide Oligomerization Domain 2 (NOD2/CARD15) as a novel HIF-1 target and 3-O-sulfo-galactoceramide (sulfatide) and Mycobacterium sp. specific sulfolipid-1 as the first NOD2 ligands that both compete for binding to NOD2. Loss of NOD2 function impaired autophagy upstream of the autophagy inhibitor chloroquine by reducing the number of acidic vesicles. Inhibition of sulfatide synthesis elicited defects in autophagy similar to the NOD2 loss of function but did not influence NOD2-mediated NF-kB signaling. CONCLUSIONS: Our findings suggest that the interaction of NOD2 with sulfatide may mediate the balance between autophagy and inflammation in hypoxic cells. GENERAL SIGNIFICANCE: These findings may lead to a better understanding of complex inflammatory pathologies like Crohn's disease and tuberculosis where both NOD2 and hypoxia are implicated.

DDX6 post-transcriptionally down-regulates miR-143/145 expression through host gene NCR143/145 in cancer cells.

In various human malignancies, widespread dysregulation of microRNA (miRNA) expression is reported to occur and affects various cell growth programs. Recent studies suggest that the expression levels of miRNAs that act as tumor suppressors are frequently reduced in cancers because of chromosome deletions, epigenetical changes, aberrant transcription, and disturbances in miRNA processing. MiR-143 and -145 are well-recognized miRNAs that are highly expressed in several tissues, but down-regulated in most types of cancers. However, the mechanism of this down-regulation has not been investigated in detail. Here, we show that DEAD-box RNA helicase 6, DDX6 (p54/RCK), post-transcriptionally down-regulated miR-143/145 expression by prompting the degradation of its host gene product, NCR143/145 RNA. In human gastric cancer cell line MKN45, DDX6 protein was abundantly expressed and accumulated in processing bodies (P-bodies). DDX6 preferentially increased the instability of non-coding RNA, NCR143/145, which encompasses the miR-143/145 cluster, and down-regulated the expression of mature miR-143/145. In human monocytic cell line THP-1, lipopolysaccharide treatment promoted the assembly of P-bodies and down-regulated the expression of NCR143/145 and its miR-143/145 rapidly. In these cells, cycloheximide treatment led to a loss of P-bodies and to an increase in NCR143/145 RNA stability, thus resulting in up-regulation of miR-143/145 expression. These data demonstrate that DDX6 contributed to the control of NCR143/145 RNA stability in P-bodies and post-transcriptionally regulated miR-143/145 expression in cancer cells.

HMG-boxes, ribosomopathies and neurodegenerative disease.

The UBTF E210K neuroregression syndrome is a predominantly neurological disorder caused by recurrent de novo dominant variants in Upstream Binding Factor, that is, essential for transcription of the ribosomal RNA genes. This unusual form of ribosomopathy is characterized by a slow decline in cognition, behavior, and sensorimotor functioning during the critical period of development. UBTF (or UBF) is a multi-HMGB-box protein that acts both as an epigenetic factor to establish "open" chromatin on the ribosomal genes and as a basal transcription factor in their RNA Polymerase I transcription. Here we review the possible mechanistic connections between the UBTF variants, ribosomal RNA gene transcription and the neuroregression syndrome, and suggest that DNA topology may play an important role.

Ribosomal RNA Transcription Machineries in Intestinal Protozoan Parasites: A Bioinformatic Analysis.

PURPOSE: Ribosome biogenesis is a key process in all living organisms, energetically expensive and tightly regulated. Currently, little is known about the components of the ribosomal RNA (rRNA) transcription machinery that are present in intestinal parasites, such as Giardia duodenalis, Cryptosporidium parvum, and Entamoeba histolytica. Thus, in the present work, an analysis was carried out looking for the components of the rRNA transcription machinery that are conserved in intestinal parasites and if these could be used to design new treatment strategies. METHODS: The different components of the rRNA transcription machinery were searched in the studied parasites with the NCBI BLAST tool in the EuPathDB Bioinformatics Resource Center database. The sequences of the RRN3 and POLR1F orthologs were aligned and important regions identified. Subsequently, three-dimensional models were built with different bioinformatic tools and a structural analysis was performed. RESULTS: Among the protozoa examined, C. parvum is the parasite with the fewest identifiable components of the rRNA transcription machinery. TBP, RRN3, POLR1A, POLR1B, POLR1C, POLR1D, POLR1F, POLR1H, POLR2E, POLR2F and POLR2H subunits were identified in all species studied. Furthermore, the interaction regions between RRN3 and POLR1F were found to be conserved and could be used to design drugs that inhibit rRNA transcription in the parasites studied. CONCLUSION: The inhibition of the rRNA transcription machinery in parasites might be a new therapeutic strategy against these microorganisms.

MLL-AF4 and a murinized pSer-variant thereof are turning on the nucleolar stress pathway.

BACKGROUND: Recent pathomolecular studies on the MLL-AF4 fusion protein revealed that the murinized version of MLL-AF4, the MLL-Af4 fusion protein, was able to induce leukemia when expressed in murine or human hematopoietic stem/progenitor cells (Lin et al. in Cancer Cell 30:737-749, 2016). In parallel, a group from Japan demonstrated that the pSer domain of the AF4 protein, as well as the pSer domain of the MLL-AF4 fusion is able to bind the Pol I transcription factor complex SL1 (Okuda et al. in Nat Commun 6:8869, 2015). Here, we investigated the human MLL-AF4 and a pSer-murinized version thereof for their functional properties in mammalian cells. Gene expression profiling studies were complemented by intracellular localization studies and functional experiments concerning their biological activities in the nucleolus. RESULTS: Based on our results, we have to conclude that MLL-AF4 is predominantly localizing inside the nucleolus, thereby interfering with Pol I transcription and ribosome biogenesis. The murinized pSer-variant is localizing more to the nucleus, which may suggest a different biological behavior. Of note, AF4-MLL seems to cooperate at the molecular level with MLL-AF4 to steer target gene transcription, but not with the pSer-murinized version of it. CONCLUSION: This study provides new insights and a molecular explanation for the described differences between hMLL-hAF4 (not leukemogenic) and hMLL-mAf4 (leukemogenic). While the human pSer domain is able to efficiently recruit the SL1 transcription factor complex, the murine counterpart seems to be not. This has several consequences for our understanding of t(4;11) leukemia which is the most frequent leukemia in infants, childhood and adults suffering from MLL-r acute leukemia.

Ayaconin, a novel inhibitor of the plasma contact system from the sand fly Lutzomyia ayacuchensis, a vector of Andean-type cutaneous leishmaniasis.

Transcriptome analysis of the salivary gland cDNA library from a phlebotomine sand fly, Lutzomyia ayacuchensis, identified a transcript coding for the PpSP15/SL1 family protein as the second most abundant salivary component. In the present study, a recombinant protein of the PpSP15/SL1 family protein, designated ayaconin, was expressed in Escherichia coli, and its biological activity was characterized. The recombinant ayaconin purified from the soluble fraction of E. coli lysate efficiently inhibited the intrinsic but not extrinsic blood coagulation pathway. When the target of ayaconin was evaluated using fluorescent substrates of coagulation factors, ayaconin inhibited factor XIIa (FXIIa) activity more efficiently in a dose-dependent manner, suggesting that FXII is the primary target of ayaconin. In addition, incubation of ayaconin with FXII prior to activation effectively inhibited FXIIa activity, whereas such inhibition was not observed when ayaconin was mixed after the production of FXIIa, indicating that ayaconin inhibits the activation process of FXII to produce FXIIa, but not the enzymatic activity of FXIIa. Moreover, ayaconin was shown to bind to FXII, suggesting that the binding of ayaconin to FXII is involved in the inhibitory mechanism against FXII activation. These results suggest that ayaconin plays an important role in the blood-sucking of Lu. ayacuchensis.

Viral and cellular translation during SARS-CoV-2 infection.

SARS-CoV-2 is a betacoronavirus that emerged in China in December 2019 and which is the causative agent of the Covid-19 pandemic. This enveloped virus contains a large positive-sense single-stranded RNA genome. In this review, we summarize the current knowledge on the molecular mechanisms for the translation of both viral transcripts and cellular messenger RNAs. Non-structural proteins are encoded by the genomic RNA and are produced in the early steps of infection. In contrast, the structural proteins are produced from subgenomic RNAs that are translated in the late phase of the infectious program. Non-structural protein 1 (NSP1) is a key molecule that regulates both viral and cellular translation. In addition, NSP1 interferes with multiple steps of the interferon I pathway and thereby blocks host antiviral responses. Therefore, NSP1 is a drug target of choice for the development of antiviral therapies.

1H, 13C and 15N assignment of stem-loop SL1 from the 5'-UTR of SARS-CoV-2.

The stem-loop (SL1) is the 5'-terminal structural element within the single-stranded SARS-CoV-2 RNA genome. It is formed by nucleotides 7-33 and consists of two short helical segments interrupted by an asymmetric internal loop. This architecture is conserved among Betacoronaviruses. SL1 is present in genomic SARS-CoV-2 RNA as well as in all subgenomic mRNA species produced by the virus during replication, thus representing a ubiquitous cis-regulatory RNA with potential functions at all stages of the viral life cycle. We present here the 1H, 13C and 15N chemical shift assignment of the 29 nucleotides-RNA construct 5_SL1, which denotes the native 27mer SL1 stabilized by an additional terminal G-C base-pair.