The coronavirus SARS-CoV-2 uses an RNA-dependent RNA polymerase (RdRp) to replicate and transcribe its genome. Previous structures of the RdRp revealed a monomeric enzyme composed of the catalytic subunit nsp12, two copies of subunit nsp8, and one copy of subunit nsp7.
Fig: Structure of antiparallel RdRp dimer: a Two views of a ribbon model of the antiparallel RdRp–RNA dimer. Color code for nsp7, nsp8, nsp12 domains (NiRAN, interface, fingers, palm, and thumb), RNA template (blue), and RNA product (red) is used throughout. Nsp7 subunits in the two RdRp monomers are colored slightly differently for the two monomers (dark and light blue, respectively). Views are related by a 90° rotation around the vertical axis. b Close-up view of nsp7–nsp7 dimerization interface. View is as in the left structure of panel a. The final cryo-EM density is shown as a black mesh.
Here we report an alternative, dimeric form of the enzyme and resolve its structure at 5.5 Å resolution. In this structure, the two RdRps contain only one copy of nsp8 each and dimerize via their nsp7 subunits to adopt an antiparallel arrangement. We speculate that the RdRp dimer facilitates template switching during production of sub-genomic RNAs.
Jochheim, F.A., Tegunov, D., Hillen, H.S. et al. The structure of a dimeric form of SARS-CoV-2 polymerase. Commun Biol 4, 999 (2021). https://doi.org/10.1038/s42003-021-02529-9