The SARS-CoV-2 NiRAN domain of nsp12 transfers RNA to the amino terminus of nsp9, forming a covalent RNA-protein intermediate, and subsequently transfers the RNA to GDP to form the core cap structure GpppA-RNA.
The study reveals an unconventional mechanism by which SARS-CoV-2 caps its RNA genome, identifying a new potential target for COVID-19 antivirals.
Abstract The RNA genome of SARS-CoV-2 contains a 5′ cap that facilitates the translation of viral proteins, protection from exonucleases and evasion of the host immune response 1–4 . How this cap is made in SARS-CoV-2 is not completely understood. Here we reconstitute the N 7- and 2′- O -methylated SARS-CoV-2 RNA cap ( 7Me GpppA 2′- O -Me ) using virally encoded non-structural proteins (nsps). We show that the kinase-like nidovirus RdRp-associated nucleotidyltransferase (NiRAN) domain 5 of nsp12 transfers the RNA to the amino terminus of nsp9, forming a covalent RNA–protein intermediate (a process termed RNAylation). Subsequently, the NiRAN domain transfers the RNA to GDP, forming the core cap structure GpppA-RNA. The nsp14 6 and nsp16 7 methyltransferases then add methyl groups to form functional cap structures. Structural analyses of the replication–transcription complex bound to nsp9 identified key interactions that mediate the capping reaction. Furthermore, we demonstrate in a reverse genetics system 8 that the N terminus of nsp9 and the kinase-like active-site residues in the NiRAN domain are required for successful SARS-CoV-2 replication. Collectively, our results reveal an unconventional mechanism by which SARS-CoV-2 caps its RNA genome, thus exposing a new target in the development of antivirals to treat COVID-19.
Park et al. (Tue,) conducted a other in SARS-CoV-2. SARS-CoV-2 non-structural proteins was evaluated on RNA capping mechanism. The SARS-CoV-2 NiRAN domain of nsp12 transfers RNA to the amino terminus of nsp9, forming a covalent RNA-protein intermediate, and subsequently transfers the RNA to GDP to form the core cap structure GpppA-RNA.