Biology subjects

Grimes, J. M.

Publications and source records attributed to Grimes, J. M..

7 recordsLinked to original sources

bioRxiv2026

Influenza A virus initiates genome selection through promoter-dependent nuclear export

Influenza A virus replicates its segmented RNA genome in the nucleus in the context of viral ribonucleoprotein (vRNP) complexes. Newly synthesised vRNPs are exported to the cytoplasm for virion assembly, whereas structurally similar complementary RNPs (cRNPs), which function as replication intermediates, are not incorporated into virions. The molecular basis for this selectivity remains unclear. Here, combining promoter mutagenesis, single-molecule fluorescence in situ hybridisation (smFISH), virus-like particle (VLP) assays and cryo-electron microscopy (cryo-EM), we find that cRNPs are retained in the nucleus and that export competence is encoded by promoter architecture, with the length of the single-stranded 3' promoter region as the principal contributing feature and promoter sequence and duplex architecture further modulating export efficiency. cRNPs carrying export-competent promoters are incorporated into virus-like particles, demonstrating a functional link between nuclear export and packaging competence. Cryo-EM analyses reveal that both 3' vRNA and cRNA promoters bind a common polymerase surface site but are associated with distinct polymerase conformational landscapes, with only the vRNA promoter being compatible with an encapsidase conformation of the polymerase. Together, our findings identify a promoter-dependent checkpoint that links RNA promoter architecture and polymerase conformation to RNP export and packaging. These results demonstrate that influenza virus initiates genome selection in the nucleus and reveal nuclear export as an early step in genome selection.

microbiology↗

bioRxiv2023

DSIF factor Spt5 coordinates transcription, maturation and exoribonucleolysis of RNA polymerase II transcripts.

The timely termination of RNA polymerase II (Pol II) transcription is critical for polymerase recycling and preventing interference with the expression of the neighbouring genes. Termination of Pol II transcription involves exoribonucleolytic decay of the nascent RNA by 5-3 exonuclease Xrn2. Xrn2 attacks the 5-PO4-end and executes degradation of the nascent RNA generated by the endonucleolytic cleavage at the poly(A) site which eventually leads to Pol II release from DNA. However, the molecular details of when and how during this process Xrn2 interacts with the Pol II elongation complex to mediate its dissociation from DNA is not understood. Here, we demonstrate that Xrn2 interacts with Pol II and Spt5, a conserved transcription factor that controls Pol II processivity and pausing. Importantly, Xrn2 activity is stimulated by Spt5 in vitro and Spt5-depleted cells show defective transcription termination. Our results support a model where Xrn2 first forms a stable complex with the elongating Pol II to acquire its full activity in degrading nascent RNA. Spt5 also promotes premature termination attenuating the expression of non-coding transcripts. By contrast, Spt5 depletion leads to Pol II retention at promoters of protein-coding genes. Pol IIs that transcribe into a gene body in the absence of Spt5 exhibit severely reduced elongation rates and defective pre-mRNA processing. We propose that Spt5 plays a major role in the production of functional mRNA by directly stimulating the activity of the RNA enzymes and preventing entry of Pol II complexes not configured to support transcription and pre-mRNA processing into elongation.

molecular biology↗

bioRxiv2023

Structural Characterization of the Full-length Hantaan Virus Polymerase

Hantaviridae are a family of segmented negative-sense RNA viruses that contains important human and animal pathogens including Andes orthohantavirus and Hantaan orthohantavirus. Hantaviridae contain a viral RNA-dependent RNA polymerase that replicates and transcribes the viral genome in the cytoplasm of infected cells. Here we establish the expression and purification of the polymerase from the Old World Hantaan orthohantavirus and characterise the structure using single particle cryo electron microscopy. We determine a series of structures at resolutions between 2.7 and 3.3 [A] of RNA free polymerase comprising the core, core and endonuclease, and a full-length polymerase. The full-length polymerase structure depicts the location of the cap binding and C-terminal domains which are arranged in a conformation that is incompatible with transcription and in a novel conformation not observed in previous conformations of cap-snatching viral polymerase. We further describe structures with 5' vRNA promoter in the presence and absence of a nucleotide triphosphate. The nucleotide bound structure mimics a replication pre-initiation complex and the nucleotide stabilises the motif E in a conformation distinct from those previously observed. We observe motif E in four distinct conformations including {beta}-sheet, two helical arrangements, and an ordered loop. The insights gained here form a starting point for future detailed mechanistic studies of both the transcription and replication activities of the hantavirus polymerase and for the development of therapeutic targets.

biochemistry↗

bioRxiv2020

A high resolution view of an adolescent flavivirus

Mosquito-transmitted flaviviruses, such as Dengue virus (DENV) or Zika virus (ZIKV), are responsible for significant economic damage and human misery. In infected cells, flaviviruses first assemble into an immature form within the endoplasmatic reticulum (ER), and then undergo further processing by furin protease in the trans-Golgi. Despite substantial efforts, previous cryogenic electron microscopy (cryo-EM) studies of immature flaviviruses were restricted to low to medium resolutions, limiting our understanding of maturation. To better grasp the process of maturation, we have carried out cryo-EM reconstructions of immature Spondweni virus (SPOV), an emerging human flavivirus belonging to the same serogroup as ZIKV (~75% amino acid identity). By combining localized reconstruction and focused refinement, we were able to improve the resolution to 3.8 [A], yielding unprecedented insight into the immature form. The structure elucidates how, at neutral pH, polar interactions conceal the furin recognition site within trimeric envelope (E) protein spikes. Furthermore, we identify how a strictly conserved pH sensor anchors the precursor membrane (prM) protein to immature E. We reconstructed mature forms of SPONV and DENV to 2.6[A] and 3.1[A], respectively. Comparison with immature virus shows a conserved binding pocket for a lipid headgroup, which forms as a consequence of the rearrangement of amphipathic stem-helices of E. We propose a structural role for the pocket and suggest it stabilizes mature E. Taken together, our data suggest a compelling rationale for low-pH triggered conformational rearrangement in the Golgi, which occurs during flavivirus maturation.

microbiology↗

bioRxiv2020

Enisamium is a small molecule inhibitor of the influenza A virus and SARS-CoV-2 RNA polymerases

Influenza A virus and coronavirus strains cause a mild to severe respiratory disease that can result in death. Although vaccines exist against circulating influenza A viruses, such vaccines are ineffective against emerging pandemic influenza A viruses. Currently, no vaccine exists against coronavirus infections, including pandemic SARS-CoV-2, the causative agent of the Coronavirus Disease 2019 (COVID-19). To combat these RNA virus infections, alternative antiviral strategies are needed. A key drug target is the viral RNA polymerase, which is responsible for viral RNA synthesis. In January 2020, the World Health Organisation identified enisamium as a candidate therapeutic against SARS-CoV-2. Enisamium is an isonicotinic acid derivative that is an inhibitor of multiple influenza B and A virus strains in cell culture and clinically approved in 11 countries. Here we show using in vitro assays that enisamium and its putative metabolite, VR17-04, inhibit the activity of the influenza virus and the SARS-CoV-2 RNA polymerase. VR17-04 displays similar efficacy against the SARS-CoV-2 RNA polymerase as the nucleotide analogue remdesivir triphosphate. These results suggest that enisamium is a broad-spectrum small molecule inhibitor of RNA virus RNA synthesis, and implicate it as a possible therapeutic option for treating SARS-CoV-2 infection. Unlike remdesivir, enisamium does not require intravenous administration which may be advantageous for the development of COVID-19 treatments outside a hospital setting. ImportanceInfluenza A virus and SARS-CoV-2 are respiratory viruses capable of causing pandemics, and the latter is responsible for the Coronavirus Disease 2019 (COVID-19) pandemic. Both viruses encode RNA polymerases which transcribe their RNA genomes and are important targets for antiviral drugs including remdesivir. Here, we show that the antiviral drug enisamium inhibits the RNA polymerases of both influenza A virus and SARS-CoV-2. Furthermore, we show that a putative metabolite of enisamium is a more potent inhibitor, inhibiting the SARS-CoV-2 RNA polymerase with similar efficiency to remdesivir. Our data offer insight into the mechanism of action for enisamium, and implicate it as a broad-spectrum antiviral which could be used in the treatment of SARS-CoV-2 infection.

microbiology↗

bioRxiv2020

Correlative cryo-structured illumination fluorescence microscopy and soft X-ray tomography elucidates reovirus intracellular release pathway

Imaging of biological matter across resolution scales presents the challenge of preserving the direct and unambiguous correlation of subject features from the macroscopic to the microscopic level. We present here a correlative imaging platform developed specifically for imaging cells in 3D, under cryogenic conditions. Rapid cryo-preservation of biological specimens is the current gold standard in sample preparation for ultrastructural analysis in X-ray imaging. However, cryogenic fluorescence localisation methods are by and large diffraction-limited and fail to deliver matching resolution. We addressed this technological gap by developing an integrated, user-friendly, platform for 3D correlative imaging of cells in cryo-preserved states using super-resolution structured illumination microscopy (SIM) in conjunction with soft X-ray tomography (SXT). The power of this new approach is demonstrated by studying the process of reovirus release from intracellular vesicles during the early stages of infection and identifying novel virus-induced structures.

cell biology↗

bioRxiv2019

Novel risk genes and mechanisms implicated by exome sequencing of 2,572 individuals with pulmonary arterial hypertension

Group 1 pulmonary arterial hypertension (PAH) is a rare disease with high mortality despite recent therapeutic advances. Pathogenic remodeling of pulmonary arterioles leads to increased pulmonary pressures, right ventricular hypertrophy and heart failure. Mutations in bone morphogenetic protein receptor type 2 and other risk genes predispose to disease, but the vast majority of non-familial cases remain genetically undefined. To identify new risk genes, we performed exome sequencing in a large cohort from the National Biological Sample and Data Repository for PAH. By statistical association of rare deleterious variants, we found tissue kallikrein 1 and gamma glutamyl carboxylase as new candidate risk genes for idiopathic PAH associated with a later age-of-onset and relatively moderate disease phenotype compared to bone morphogenetic receptor type 2. Both genes play important roles in vascular hemodynamics and inflammation but have not been implicated in PAH previously. These data suggest new genes, pathogenic mechanisms and therapeutic targets for this lethal vasculopathy.

genetics↗