Biology subjects

te Velthuis, A. J. W.

Publications and source records attributed to te Velthuis, A. J. W..

21 records · Page 2Linked to original sources

bioRxiv2021

A SARS-CoV-2 mini-genome assay based on negative-sense RNA to study replication inhibitors and emerging mutations

Severe Acute Respiratory Coronavirus 2 (SARS-CoV-2) is a positive-sense single-stranded RNA virus and the causative agent of the Coronavirus disease 2019 (COVID-19) pandemic. Efforts to identify inhibitors of SARS-CoV-2 replication enzymes and better understand the mechanisms underlying viral RNA synthesis have largely relied on biosafety level 3 (BSL3) laboratories, limiting throughput and accessibility. Recently, replicon systems have been proposed that involve ~30 kb RNA-based replicons or large plasmids that express the viral structural and non-structural proteins (nsp) in addition to a positive-sense reporter RNA. Unfortunately, these assays are not user-friendly due to plasmid instability or a poor signal to background ratio. We here present a simple mini-genome assay consisting of a ~2.5 kb-long negative-sense, nanoluciferase-encoding sub-genomic reporter RNA that is expressed from a plasmid, and amplified and transcribed by the SARS-CoV-2 RNA polymerase core proteins nsp7, nsp8 and nsp12. We show that expression of nsp7, 8 and 12 is sufficient to obtain robust positive- and negative-sense RNA synthesis in cell culture, that addition of other nsps modulates expression levels, and that replication of the reporter RNA can be inhibited by active site mutations in nsp12 or the SARS-CoV-2 replication inhibitor remdesivir. The mini-genome assay provides a signal that is 170-fold above background on average, providing excellent sensitivity for high-throughput screens, while the use of small plasmids facilitates site-directed mutagenesis for fundamental analyses of SARS-CoV-2 RNA synthesis. Importance statementThe impact of the COVID-19 pandemic has made it essential to better understand the basic biology of SARS-CoV-2, and to search for compounds that can block the activity of key SARS-CoV-2 replication enzymes. However, studies with live SARS-CoV-2 require biosafety level 3 facilities, while existing replicon systems depend on long positive-sense subgenomes that are often difficult to manipulate or produce a high background signal, limiting drug-screens and a rapid analysis of emerging SARS-CoV-2 mutations during the COVID-19 pandemic. To make it easier to study emerging SARS-CoV-2 mutants and screen for inhibitors, we developed a simple mini-replicon that produces a minimal background signal, that can be used in any tissue culture lab, and that only requires four small plasmids to work.

microbiology↗

bioRxiv2021

The host factor ANP32A is required for influenza A virus vRNA and cRNA synthesis

Influenza A viruses are negative-sense RNA viruses that rely on their own viral replication machinery to replicate and transcribe their segmented single-stranded RNA genome. The viral ribonucleoprotein complexes in which viral RNA is replicated consist of a nucleoprotein scaffold around which the RNA genome is bound, and a heterotrimeric RNA-dependent RNA polymerase that catalyzes viral replication. The RNA polymerase copies the viral RNA (vRNA) via a replicative intermediate, called the complementary RNA (cRNA), and subsequently uses this cRNA to make more vRNA copies. To ensure that new cRNA and vRNA molecules are associated with ribonucleoproteins in which they can be amplified, the active RNA polymerase recruits a second polymerase to encapsidate the cRNA or vRNA. Host factor ANP32A has been shown to be essential for viral replication and to facilitate the formation of a dimer between viral RNA polymerases and differences between mammalian and avian ANP32A proteins are sufficient to restrict viral replication. It has been proposed that ANP32A is only required for the synthesis of vRNA molecules from a cRNA, but not vice versa. However, this view does not match recent molecular evidence. Here we use minigenome assays, virus infections, and viral promoter mutations to demonstrate that ANP32A is essential for both vRNA and cRNA synthesis. Moreover, we show that ANP32 is not only needed for the actively replicating polymerase, but also for the polymerase that is encapsidating nascent viral RNA products. Overall, these results provide new insights into influenza A virus replication and host adaptation. IMPORTANCEZoonotic avian influenza A viruses pose a constant threat to global health and they have the potential to cause highly pathogenic pandemic outbreaks. Species variations in host factor ANP32A play a key role in supporting the activity of avian influenza A virus RNA polymerases in mammalian hosts. Here we show that ANP32A acts at two stages in the influenza A virus replication cycle, supporting recent structural experiments and in line with its essential role. Understanding how ANP32A supports viral RNA polymerase activity and how it supports avian polymerase function in mammalian hosts is important for understanding influenza A virus replication and the development of antiviral strategies against influenza A viruses.

microbiology↗

bioRxiv2019

Real-time analysis of single influenza virus replication complexes reveals large promoter-dependent differences in initiation dynamics

The viral RNA (vRNA) genome of influenza viruses is replicated by the RNA-dependent RNA polymerase (RNAP) via a complementary RNA (cRNA) intermediate. The vRNA promoter can adopt multiple conformations when bound by the RNAP. However, the dynamics, determinants, and biological role of these conformations are unknown; further, little is known about cRNA promoter conformations. To probe the RNA conformations adopted during initial replication, we monitored single, surface-immobilised vRNA and cRNA initiation complexes in real-time. Our results show that, while the 3 terminus of the vRNA promoter exists in dynamic equilibrium between pre-initiation and initiation conformations, the cRNA promoter exhibited very limited dynamics. Two residues in the proximal 3 region of the cRNA promoter (residues absent in the vRNA promoter) allowed the cRNA template strand to reach further into the active site, limiting promoter dynamics. Our results highlight promoter-dependent differences in influenza initiation mechanisms, and advance our understanding of virus replication.

microbiology↗