RNA-dependent RNA Polymerase Research Articles

HSP90 is part of a protein complex with the L polymerase of Rift Valley fever phlebovirus and prevents its degradation by the proteasome during the viral genome replication/transcription stage

The mosquito-borne Rift Valley fever virus (RVFV) from the Phenuiviridae family is a single-stranded RNA virus that causes the re-emerging zoonotic disease Rift Valley fever (RVF). Classified as a Category A agent by the NIH, RVFV infection can cause debilitating disease or death in humans and lead to devastating economic impacts by causing abortion storms in pregnant cattle. In a previous study, we showed that the host chaperone protein HSP90 is an RVFV-associated host factor that plays a critical role post viral entry, during the active phase of viral genome replication/transcription. In this study, we have elucidated the molecular mechanisms behind the regulatory effect of HSP90 during infection with RVFV. Our results demonstrate that during the early infection phase, host HSP90 associates with the viral RNA-dependent RNA polymerase (L protein) and prevents its degradation through the proteasome, resulting in increased viral replication.

Characterization of two novel fusariviruses co-infecting a single isolate of phytopathogenic fungus Botrytis cinerea.

A wide diversity of mycoviruses has been reported from Botrytis species, some with the potential to suppress the pathogenic abilities of this fungus. Considering their importance, this study was devised to find potential hypovirulence-associated mycoviruses found in Botrytis cinerea strains isolated from Pakistani strawberry fields. Here we report the complete genome characterization of two fusariviruses co-infecting a single isolate of phytopathogenic fungus B. cinerea (Kst14a). The viral genomes were sequenced by deep sequencing using total RNA fractions of the Kst14a isolate. The identified viruses were tentatively namedBotrytis cinerea fusarivirus 9 (BcFV9) and Botrytis cinerea fusarivirus 3a (BcFV3a). Both viruses had a single-segmented (ssRNA) genome having a size of 6424 and 8370 nucleotides encoding two discontinuous open reading frames (ORFs). ORF-1 of both mycoviruses encodes for a polyprotein having a conserved domain of RNA-dependent RNA polymerase (RdRP) and a helicase domain (Hel) which function in RNA replication, while ORF2 encodes a hypothetical protein with an unknown function, respectively. Phylogenetic analysis indicated that BcFV9 made a clade with the genus Alphafusarivirus and BcFV3a fall in the genus Betafusarivirus in the family Fusariviridae. To our knowledge, this is the first report of two fusariviruses identified in isolates of B. cinerea from Pakistan. Both mycoviruses successfully transfected to a compatible strain of B. cinerea (Mst11). A comparison of virus-free (VF) and virus-infected (VI) isogenic lines showed the presence of these viruses was causing hypovirulence in infected strains. Virus-infected strains also had a small lesion size while testing the pathogenicity via apple assay.

Computer-aided designing of a novel multi‑epitope DNA vaccine against severe fever with thrombocytopenia syndrome virus

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne viral disease caused by the SFTS virus (Dabie bandavirus), which has become a substantial risk to public health. No specific treatment is available now, that calls for an effective vaccine. Given this, we aimed to develop a multi-epitope DNA vaccine through the help of bioinformatics. The final DNA vaccine was inserted into a special plasmid vector pVAX1, consisting of CD8+ T cell epitopes, CD4+ T cell epitopes and B cell epitopes (six epitopes each) screened from four genome-encoded proteins——nuclear protein (NP), glycoprotein (GP), RNA-dependent RNA polymerase (RdRp), as well as nonstructural protein (NSs). To ascertain if the predicted structure would be stable and successful in preventing infection, an immunological simulation was run on it. In conclusion, we designed a multi-epitope DNA vaccine that is expected to be effective against Dabie bandavirus, but in vivo trials are needed to verify this claim.

Structural snapshots of phenuivirus cap-snatching and transcription.

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a human pathogen that is now endemic to several East Asian countries. The viral large (L) protein catalyzes viral transcription by stealing host mRNA caps via a process known as cap-snatching. Here, we establish an in vitro cap-snatching assay and present three high-quality electron cryo-microscopy (cryo-EM) structures of the SFTSV L protein in biologically relevant, transcription-specific states. In a priming-state structure, we show capped RNA bound to the L protein cap-binding domain (CBD). The L protein conformation in this priming structure is significantly different from published replication-state structures, in particular the N- and C-terminal domains. The capped-RNA is positioned in a way that it can feed directly into the RNA-dependent RNA polymerase (RdRp) ready for elongation. We also captured the L protein in an early-elongation state following primer-incorporation demonstrating that this priming conformation is retained at least in the very early stages of primer extension. This structural data is complemented by in vitro biochemical and cell-based assays. Together, these insights further our mechanistic understanding of how SFTSV and other bunyaviruses incorporate stolen host mRNA fragments into their viral transcripts thereby allowing the virus to hijack host cell translation machinery.

Lung-targeted delivery of nsp12 siRNAs restores host type I interferon responses

The RNA-dependent RNA polymerase (RdRp) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), known as nsp12, is crucial to viral replication and spread. Being one of the most conserved proteins of SARS-CoV-2, nsp12 is also a promising therapeutic target for COVID-19. In addition, nsp12 has been reported to suppress the host type I interferon (IFN-I) responses. We used HEK293T cells exogenously expressing nsp12-luciferase to identify siRNAs against nsp12. A series of in vitro and in vivo experiments were employed to examine the effect of RBD-11b-modified cationic liposomes (CLs) on targeted delivery of siRNAs to the mouse lungs. Mice were airway-administered adenovirus to induce the exogenous expression of nsp12 in the mouse lungs, followed by nsp12 siRNAs@RBD-11b-CLs treatment. Nsp12 expression and the activity of the IRF3/IFN-I axis in the lungs were then examined. High-efficiency nsp12 siRNAs were identified and successfully delivered to the mouse lungs by the RBD-11b-modified CLs. The nsp12 siRNAs@RBD-11b-CLs efficiently inhibited the exogenous expression of nsp12 in the mouse lungs. Moreover, nsp12 siRNAs@ RBD-11b-CLs successfully restored the nucleus transport of IRF3, thereby increasing the expression of IFNβ and several IFN effector genes in alveolar cells. We establish a lung targeting system to efficiently deliver siRNAs against SARS-CoV-2 nsp12 and significantly restore host type I interferon responses. This study will provide fresh perspectives and forthcoming approaches for the treatment of COVID-19 and other RNA viruses.

In Vivo Delivery of Spherical and Cylindrical In Vitro Reconstituted Virus-like Particles Containing the Same Self-Amplifying mRNA.

The dramatic effectiveness of recent mRNA (mRNA)-based COVID vaccines delivered in lipid nanoparticles has highlighted the promise of mRNA therapeutics in general. In this report, we extend our earlier work on self-amplifying mRNAs delivered in spherical in vitro reconstituted virus-like particles (VLPs), and on drug delivery using cylindrical virus particles. In particular, we carry out separate in vitro assemblies of a self-amplifying mRNA gene in two different virus-like particles: one spherical, formed with the capsid protein of cowpea chlorotic mottle virus (CCMV), and the other cylindrical, formed from the capsid protein of tobacco mosaic virus (TMV). The mRNA gene is rendered self-amplifying by genetically fusing it to the RNA-dependent RNA polymerase (RdRp) of Nodamura virus, and the relative efficacies of cell uptake and downstream protein expression resulting from their CCMV- and TMV-packaged forms are compared directly. This comparison is carried out by their transfections into cells in culture: expressions of two self-amplifying genes, enhanced yellow fluorescent protein (EYFP) and Renilla luciferase (Luc), packaged alternately in CCMV and TMV VLPs, are quantified by fluorescence and chemiluminescence levels, respectively, and relative numbers of the delivered mRNAs are measured by quantitative real-time PCR. The cellular uptake of both forms of these VLPs is further confirmed by confocal microscopy of transfected cells. Finally, VLP-mediated delivery of the self-amplifying-mRNA in mice following footpad injection is shown by in vivo fluorescence imaging to result in robust expression of EYFP in the draining lymph nodes, suggesting the potential of these plant virus-like particles as a promising mRNA gene and vaccine delivery modality. These results establish that both CCMV and TMV VLPs can deliver their in vitro packaged mRNA genes to immune cells and that their self-amplifying forms significantly enhance in situ expression. Choice of one VLP (CCMV or TMV) over the other will depend on which geometry of nucleocapsid is self-assembled more efficiently for a given length and sequence of RNA, and suggests that these plant VLP gene delivery systems will prove useful in a wide variety of medical applications, both preventive and therapeutic.

The nucleoside analog 4'-fluorouridine suppresses the replication of multiple enteroviruses by targeting 3D polymerase.

Human enteroviruses are the major pathogens causing hand-foot-and-mouth disease in infants and young children throughout the world, and infection with enterovirus is also associated with severe complications, such as aseptic meningitis and myocarditis. However, there are no antiviral drugs available to treat enteroviruses infection at present. In this study, we found that 4'-fluorouridine (4'-FlU), a nucleoside analog with low cytotoxicity, exhibited broad-spectrum activity against infections of multiple enteroviruses with EC50 values at low micromolar levels, including coxsackievirus A10 (CV-A10), CV-A16, CV-A6, CV-A7, CV-B3, enterovirus A71 (EV-A71), EV-A89, EV-D68, and echovirus 6. With further investigation, the results indicated that 4'-FlU directly interacted with the RNA-dependent RNA polymerase of enterovirus, the 3D pol, and impaired the polymerase activity of 3D pol, hence inhibiting viral RNA synthesis and significantly suppressing viral replication. Our findings suggest that 4'-FlU could be promisingly developed as a broad-spectrum direct-acting antiviral agent for anti-enteroviruses therapy.

The artificial production of viral-like particles in Nicotiana benthamiana suggests the pro-assembly role of the Cannabis cryptic virus RdRP

AbstractThe partitivirids feature an icosahedral protein coating accommodating both their dsRNA genome and RNA-dependent RNA polymerase (RdRP). This signifies that transcription and replication activities of the viral polymerase occur within the capsid, emphasizing that the viral cycle relies on polymerase incorporation. Particles lacking RdRP are defective and hence non-infectious. Encapsidation and replication are intricately linked for dsRNA viruses, to the extent that, for many of these, such as the cystovirids, the RdRP serves a dual role as a transcriptase/replicase and a pro-assembly factor, ensuring structural stability and overall capsid integrity. This work investigates if RdRP has a similar role within the capsid of Cannabis cryptic virus (CanCV), a betapartitivirus affecting Cannabis sativa. Utilizing reverse genetics in Nicotiana benthamiana, we conclusively established that RdRP expression is indispensable for CanCV’s virus-like particle formation. This study enhances our understanding of CanCV encapsidation, with RdRP serving a pivotal role as a pro-assembly factor. These preliminary findings contribute to the knowledge of viral assembly within the Partitiviridae family.

Structure-Based Virtual Screening of Antiviral Compounds Targeting the Norovirus RdRp Protein

Background: Human noroviruses (NV) are the primary etiological organisms causing acute gastroenteritis around the world, causing severe morbidity and imposing a significant economic burden. The RNA-dependent RNA polymerase (RdRp) is essential for viral replication and could be a promising target for anti-NV therapeutics. Despite the discovery of a few NV RdRp inhibitors, the majority of these pharmaceuticals have demonstrated limited efficacy in inhibiting viral replication in cellular models.Methods: In this study, computational screening of antiviral compounds was conducted targeting the NV RdRp protein. The assessment was based on binding poses and the key residues of RdRp involved in interactions with compounds.Results: The compounds namely, Ribavirin, BMS806, Dihydromyricetin, R7935788, and LY2784544 were found to bind the RdRp protein with high affinity. Notably, these compounds displayed significantly lower binding affinities compared to the positive control, PPNDS. In addition, these compounds exhibited many RdRp protein binding residues that were also present in the PPNDS.Conclusion: The results presented here suggest that these compounds have the potential to be used as inhibitors of NV RdRp in the development of antiviral medications. Nevertheless, due to the computational nature of this study, it is imperative to do experimental validation.Keywords: Noroviruses; RdRp; Virtual screening; Antiviral Compounds

Dynamic diversity of SARS-CoV-2 genetic mutations in a lung transplantation patient with persistent COVID-19.

Numerous SARS-CoV-2 variant strains with altered characteristics have emerged since the onset of the COVID-19 pandemic. Remdesivir (RDV), a ribonucleotide analogue inhibitor of viral RNA polymerase, has become a valuable therapeutic agent. However, immunosuppressed hosts may respond inadequately to RDV and develop chronic persistent infections. A patient with respiratory failure caused by interstitial pneumonia, who had undergone transplantation of the left lung, developed COVID-19 caused by Omicron BA.5 strain with persistent chronic viral shedding, showing viral fusogenicity. Genome-wide sequencing analyses revealed the occurrence of several viral mutations after RDV treatment, followed by dynamic changes in the viral populations. The C799F mutation in nsp12 was found to play a pivotal role in conferring RDV resistance, preventing RDV-triphosphate from entering the active site of RNA-dependent RNA polymerase. The occurrence of diverse mutations is a characteristic of SARS-CoV-2, which mutates frequently. Herein, we describe the clinical case of an immunosuppressed host in whom inadequate treatment resulted in highly diverse SARS-CoV-2 mutations that threatened the patient's health due to the development of drug-resistant variants.

Factor-Dependent Internal Ribosome Entry Site and -1 Programmed Frameshifting Signal in the Bemisia-Associated Dicistrovirus 2

The dicistrovirus intergenic (IGR) IRES uses the most streamlined translation initiation mechanism: the IRES recruits ribosomes directly without using protein factors and initiates translation from a non-AUG codon. Several subtypes of dicistroviruses IRES have been identified; typically, the IRESs adopt two -to three overlapping pseudoknots with key stem-loop and unpaired regions that interact with specific domains of the ribosomal 40S and 60S subunits to direct translation. We previously predicted an atypical IGR IRES structure and a potential -1 programmed frameshift (-1 FS) signal within the genome of the whitefly Bemisia-associated dicistrovirus 2 (BaDV-2). Here, using bicistronic reporters, we demonstrate that the predicted BaDV-2 -1 FS signal can drive -1 frameshifting in vitro via a slippery sequence and a downstream stem-loop structure that would direct the translation of the viral RNA-dependent RNA polymerase. Moreover, the predicted BaDV-2 IGR can support IRES translation in vitro but does so through a mechanism that is not typical of known factorless dicistrovirus IGR IRES mechanisms. Using deletion and mutational analyses, the BaDV-2 IGR IRES is mapped within a 140-nucleotide element and initiates translation from an AUG codon. Moreover, the IRES does not bind directly to purified ribosomes and is sensitive to eIF2 and eIF4A inhibitors NSC1198983 and hippuristanol, respectively, indicating an IRES-mediated factor-dependent mechanism. Biophysical characterization suggests the BaDV-2 IGR IRES contains several stem-loops; however, mutational analysis suggests a model whereby the IRES is unstructured or adopts distinct conformations for translation initiation. In summary, we have provided evidence of the first -1 FS frameshifting signal and a novel factor-dependent IRES mechanism in this dicistrovirus family, thus highlighting the diversity of viral RNA-structure strategies to direct viral protein synthesis.

Antiviral Activity of Low-Molecular-Weight Fluorinated Compounds Against Influenza A (H1N1) Virus

Influenza A virus takes a stable position in annual acute respiratory disease outbreaks during the autumn-winter period. Antiviral drugs for influenza infection help significantly ease the course of the disease and prevent complications, but there is still no drug to which none of the circulating strains would be resistant. Therefore, the search for new effective drugs against influenza A virus is constantly being conducted, in particular among fluorine-containing organic compounds, taking into account the special properties of fluorine. The goal of the study is to investigate the activity of a group of low-molecular-weight fluorinated compounds against the influenza A (H1N1) virus and to determine the potential mechanism of their action using in silico methods. Methods. Five fluorinated compounds designated as 10S-45, 10S-46, 10S-47, 10S-48 and 10S-49 were studied. In vitro experiments were performed using MDCK cell culture, A/FM/1/47 strain of influenza A (H1N1) virus, and oseltamivir phosphate as a reference drug. The cytotoxic effect on cell culture was determined using the MTT test. Antiviral effect was investigated by post-exposure incubation of compound solutions with cells, and visualization of results was performed using crystal violet dye. The possibility of the interaction of compounds with the cap-binding domain (CBD) of the PB2 subunit of the RNA-dependent RNA polymerase (RdRp) of the virus was evaluated using molecular dynamics simulation. Results. It was established that the studied compounds have a moderate cytotoxic effect on MDCK cell culture: the calculated CC50 values are in the range of 471─577 μg/mL for 10S-45, 10S-46, 10S-47 and 10S-48. Substance 10S-49 is almost 2 times less toxic compared to the rest, but it also has no effect on the influenza virus. Compounds 10S-45, 10S-46 and 10S-48 demonstrate antiviral activity in the range of 12─78 % inhibition of viral reproduction with an inverse dose-dependent effect. Substance 10S-47 showed a relatively stable inhibition of viral reproduction in the range of 63─69 % at all tested concentrations, which is similar to the results of the reference drug. According to the results of the selectivity index calculation, compound 10S-48 has the highest value, and 10S-47 has the lowest one, for the rest of the substances, this indicator is acceptable, but low, compared to the reference drug. For in silico studies, all possible spatial forms of the compounds presented as a mixture of diastereoisomers were generated: 4 stereoisomers each for 10S-45 and 10S-46, as well as 3 for 10S-47. According to the results of molecular docking of substances to the active center of CBD, 10S-45 has the lowest calculated affinity, and 10S-47 has the highest. Accordingly, compound 10S-45 showed no tendency to form ordered interactions with CBD. The 10S-47/CBD complex was not characterized by the presence of stable orientational bonds between receptor and ligand, similar to 10S-48/CBD. However, compound 10S-46 showed a generally stable interaction with CBD, albeit with a period of conformational instability. Conclusions. All studied compounds (except for 10S-49) demonstrate an antiviral effect in vitro against the influenza A (H1N1) virus. Based on the results of the in silico analysis of their interactions with CBD PB2, compound 10S-46 is highly likely to be an inhibitor of the cap-binding activity of RdRp.

CK1 and PP1 regulate Rift Valley fever virus genome replication through L protein phosphorylation

Rift Valley fever virus (RVFV) is an arbovirus in the Phenuiviridae family identified initially by the large ‘abortion storms’ observed among ruminants; RVFV can also infect humans. In humans, there is a wide variation of clinical symptoms ranging from subclinical to mild febrile illness to hepatitis, retinitis, delayed-onset encephalitis, or even hemorrhagic fever. The RVFV is a tri-segmented negative-sense RNA virus consisting of S, M, and L segments. The L segment encodes the RNA-dependent RNA polymerase (RdRp), termed the L protein, which is responsible for both viral mRNA synthesis and genome replication. Phosphorylation of viral RdRps is known to regulate viral replication. This study shows that RVFV L protein is serine phosphorylated and identified Casein Kinase 1 alpha (CK1α) and protein phosphatase 1 alpha (PP1α) as L protein binding partners. Inhibition of CK1 and PP1 through small molecule inhibitor treatment, D4476 and 1E7-03, respectively, caused a change in the phosphorylated status of the L protein. Inhibition of PP1α resulted in increased L protein phosphorylation whereas inhibition of CK1α decreased L protein phosphorylation. It was also found that in RVFV infected cells, PP1α localized to the cytoplasmic compartment. Treatment of RVFV infected cells with CK1 inhibitors reduced virus production in both mammalian and mosquito cells. Lastly, inhibition of either CK1 or PP1 reduced viral genomic RNA levels. These data indicate that L protein is phosphorylated and that CK1 and PP1 play a crucial role in regulating the L protein phosphorylation cycle, which is critical to viral RNA production and viral replication.

Molecular characterization of the complete genome of a novel ormycovirus infecting the ectomycorrhizal fungus Hortiboletus rubellus.

Advancements in high-throughput sequencing and the development of new bioinformatics tools for large-scale data analysis play a crucial role in uncovering virus diversity and enhancing our understanding of virus evolution. The discovery of the ormycovirus clades, a group of RNA viruses that are phylogenetically distinct from all known Riboviria members and are found in fungi, highlights the value of these tools for the discovery of novel viruses. The aim of this study was to examine viral populations in fungal hosts to gain insights into the diversity, evolution, and classification of these viruses. Here, we report the molecular characterization of a newly discovered ormycovirus, which we have named "Hortiboletus rubellus ormycovirus 1" (HrOMV1), that was found in the ectomycorrhizal fungus Hortiboletus rubellus. The bipartite genome of HrOMV1, whose nucleotide sequence was determined by HTS and RLM-RACE, consists of two RNA segments (RNA1 and RNA2) that exhibit similarity to those of previously studied ormycoviruses in their organization and the proteins they encode. The presence of upstream, in-frame AUG triplets in the 5' termini of both RNA segments suggests that HrOMV1, like certain other ormycoviruses, employs a non-canonical translation initiation strategy. Phylogenetic analysis showed that HrOMV1 is positioned within the gammaormycovirus clade. Its putative RNA-dependent RNA polymerase (RdRp) exhibits sequence similarity to those of other gammaormycovirus members, the most similarity to that of Termitomyces ormycovirus 1, with 33.05% sequence identity. This protein was found to contain conserved motifs that are crucial for RNA replication, including the distinctive GDQ catalytic triad observed in gammaormycovirus RdRps. The results of this study underscore the significance of investigating the ecological role of mycoviruses in mycorrhizal fungi. This is the first report of an ormycovirus infecting a member of the ectomycorrhizal genus Hortiboletus.

Comprehensive structural and functional analysis of Patuletin as a potent inhibitor of SARS-CoV-2 targeting the RNA-dependent RNA polymerases

In the pursuit of identifying effective inhibitors against SARS-CoV-2, we conducted a detailed investigation into the binding interactions and inhibitory potential of Patuletin targeting the RNA-Dependent RNA Polymerase (RdRp), comparing it with the well-known anti-RdRp agent, Remdesivir. Superimposition molecular docking studies uncovered a high degree of similarity in binding modes between Patuletin and Remdesivir within the active site of the RdRp. MD simulations (RMSD, RMSF, RG, SASA, hydrogen bonding) over a 200 ns trajectory provided valuable insights into the binding and interactions of Patuletin and RdRp comparing Remdesivir. These simulations validated the correct binding and optimum changes in both energetic and dynamic aspects, confirming the stability of the Patuletin-RdRp complex comparing the Remdesivir-RdRp complex. Further, the MM-GBSA technique revealed favorable binding energies, with Patuletin displaying a significantly lower value (-4.24 kcal/mol) compared to Remdesivir (-2.15 kcal/mol), affirming the robustness of Patuletin-RdRp binding. The MM-GBSA analysis additionally examined the binding energetic components, revealing a high degree of similarity between Patuletin and Remdesivir. 3D binding interactions were investigated through ProLIF and PLIP studies reinforcing the stable binding observed in the simulations. Principal component analysis of trajectories (PCAT) studies were employed to discern coordinated motions within the evaluated systems, providing additional perspectives on the dynamic behavior of the Patuletin-RdRp complex. In vitro assays demonstrated Patuletin's exceptional inhibitory potency against the RdRp, with an IC50 of 248 nM, far surpassing Remdesivir, which exhibited an IC50 of 20 µM. Interestingly, the in vitro IC50 against SARS-CoV-2 values further supported the superior efficacy of Patuletin (0.476 µg/ml) over Remdesivir (10.86 µg/ml). Furthermore, the viral selectivity index (SI) values highlighted the remarkable safety margin of Patuletin (SI: 790.76) compared to Remdesivir (SI: 5.87), underscoring the potential of Patuletin as a safer and more potent therapeutic agent against SARS-CoV-2. In conclusion, our comprehensive analysis presents Patuletin as a promising candidate for further exploration as a potent inhibitor of SARS-CoV-2 RdRp, offering valuable insights for the development of effective anti-COVID-19 therapies.

NeoRdRp2 with improved seed data, annotations, and scoring

RNA-dependent RNA polymerase (RdRp) is a marker gene for RNA viruses; thus, it is widely used to identify RNA viruses from metatranscriptome data. However, because of the high diversity of RdRp domains, it remains difficult to identify RNA viruses using RdRp sequences. To overcome this problem, we created a NeoRdRp database containing 1,182 hidden Markov model (HMM) profiles utilizing 12,502 RdRp domain sequences. Since the development of this database, more RNA viruses have been discovered, mainly through metatranscriptome sequencing analyses. To identify RNA viruses comprehensively and specifically, we updated the NeoRdRp by incorporating recently reported RNA viruses. To this end, 557,197 RdRp-containing sequences were used as seed RdRp datasets. These sequences were processed through deduplication, clustering, alignment, and splitting, thereby generating 19,394 HMM profiles. We validated the updated NeoRdRp database, using the UniProtKB dataset and found that the recall and specificity rates were improved to 99.4% and 81.6%, from 97.2% and 76.8% in the previous version, respectively. Comparisons of eight different RdRp search tools showed that NeoRdRp2 exhibited balanced RdRp and nonspecific detection power. Expansion of the annotated RdRp datasets is expected to further accelerate the discovery of novel RNA viruses from various transcriptome datasets. The HMM profiles of NeoRdRp2 and their annotations are available at https://github.com/shoichisakaguchi/NeoRdRp.

Targeted accurate RNA consensus sequencing (tARC-seq) reveals mechanisms of replication error affecting SARS-CoV-2 divergence.

RNA viruses, like SARS-CoV-2, depend on their RNA-dependent RNA polymerases (RdRp) for replication, which is error prone. Monitoring replication errors is crucial for understanding the virus's evolution. Current methods lack the precision to detect rare de novo RNA mutations, particularly in low-input samples such as those from patients. Here we introduce a targeted accurate RNA consensus sequencing method (tARC-seq) to accurately determine the mutation frequency and types in SARS-CoV-2, both in cell culture and clinical samples. Our findings show an average of 2.68 × 10-5 de novo errors per cycle with a C > T bias that cannot be solely attributed to APOBEC editing. We identified hotspots and cold spots throughout the genome, correlating with high or low GC content, and pinpointed transcription regulatory sites as regions more susceptible to errors. tARC-seq captured template switching events including insertions, deletions and complex mutations. These insights shed light on the genetic diversity generation and evolutionary dynamics of SARS-CoV-2.

HBCVTr: an end-to-end transformer with a deep neural network hybrid model for anti-HBV and HCV activity predictor from SMILES

Hepatitis B and C viruses (HBV and HCV) are significant causes of chronic liver diseases, with approximately 350 million infections globally. To accelerate the finding of effective treatment options, we introduce HBCVTr, a novel ligand-based drug design (LBDD) method for predicting the inhibitory activity of small molecules against HBV and HCV. HBCVTr employs a hybrid model consisting of double encoders of transformers and a deep neural network to learn the relationship between small molecules’ simplified molecular-input line-entry system (SMILES) and their antiviral activity against HBV or HCV. The prediction accuracy of HBCVTr has surpassed baseline machine learning models and existing methods, with R-squared values of 0.641 and 0.721 for the HBV and HCV test sets, respectively. The trained models were successfully applied to virtual screening against 10 million compounds within 240 h, leading to the discovery of the top novel inhibitor candidates, including IJN04 for HBV and IJN12 and IJN19 for HCV. Molecular docking and dynamics simulations identified IJN04, IJN12, and IJN19 target proteins as the HBV core antigen, HCV NS5B RNA-dependent RNA polymerase, and HCV NS3/4A serine protease, respectively. Overall, HBCVTr offers a new and rapid drug discovery and development screening method targeting HBV and HCV.

Genome-wide identification and expression analyses of the Dicer-like, Argonaute and RNA-dependent RNA polymerase gene families in onion (Allium cepa L.)

ABSTRACT RNA silencing is a highly conserved gene expression regulatory mechanism participating in plant development and stress responses. Dicer-like protein (DCL), Argonaute protein (AGO) and RNA-dependent RNA polymerase (RDR) are directly involved in RNA silencing. So far, the characterisation and expression analysis of RDR, AGO and DCL proteins have not been performed in onion. A genome-wide analysis identified eight AcAGO, four AcDCL and four AcRDR putative genes in onion. Their cis-acting elements were investigated. The transcript levels of genes in different onion tissues and response to abiotic stress were studied. The results demonstrated that AcAGOs, AcDCLs and AcRDRs showed various tissue expression patterns. AcAGO2 and AcAGO4b were highly expressed in onion bulbs. AcDCLs and AcRDRs showed the highest transcript levels in inflorescence. AcAGO1, AcAGO5 and AcDCL1 were constitutively expressed in leaf and bulb during onion bulb expansion. AcRDR1 and AcRDR6 were upregulated during bulb expansion. AcAGOs were upregulated with salinity treatment, whereas AcDCLs and AcRDRs showed different expression patterns in abiotic stress response. Our results provided a basis for further clarification of RNA silencing-mediated environment stimulation response and development in onion.

Characterization of a novel gammapartitivirus infecting the phytopathogenic fungus Pyricularia oryzae.

In this study, we identified a novel double-strand RNA (dsRNA) mycovirus in Pyricularia oryzae, designated "Magnaporthe oryzae partitivirus 4" (MoPV4). The genome of MoPV4 consists of a dsRNA-1 segment encoding an RNA-dependent RNA polymerase (RdRP) and a dsRNA-2 segment encoding a capsid protein (CP). Phylogenetic analysis indicated that MoPV4 belongs to the genus Gammapartitivirus within family Partitiviridae. The particles of MoPV4 are isometric with a diameter of about 32.4 nm. Three-dimensional structure predictions indicated that the RdRP of MoPV4 forms a classical right-handed conformation, while the CP has a reclining-V shape.