Impact of an Oxidative RNA Lesion on in vitro Replication Catalyzed by SARS-CoV-2 RNA-dependent RNA Polymerase

The production of reactive oxygen species in response to RNA virus infection results in the oxidation of viral genomic RNA within infected cells. These oxidative RNA lesions undergo replication catalyzed by the viral replisome. G to U transversion mutations are frequently observed in the SARS-CoV-2 genome and may be linked to the replication process catalyzed by RNA-dependent RNA polymerase (RdRp) past the oxidative RNA lesion 7,8-dihydro-8-oxo-riboguanosine (8-oxo-rG). To better understand the mechanism of viral RNA mutagenesis, it is crucial to elucidate the role of RdRp in replicating across oxidative lesions. In this study, we investigated the RNA synthesis catalyzed by the reconstituted SARS-CoV-2 RdRp past a single 8-oxo-rG. The RdRp-mediated primer extension was significantly inhibited by 8-oxo-rG on the template RNA. During the blockage of the extension reaction, the rate of product release by RdRp was extremely slow, indicating that the RdRp machinery remained bound to the replicating primer/template RNA. Once RdRp was able to bypass 8-oxo-rG, it preferentially incorporated rCMP, with a lesser amount of rAMP opposite 8-oxo-rG. In contrast, RdRp demonstrated greater activity in extending from the mutagenic rA:8-oxo-rG terminus compared to the lower efficiency of extension from the rC:8-oxo-rG pair. Based on steady-state kinetic analyses for the incorporation of rNMPs opposite 8-oxo-rG and chain extension from rC:8-oxo-rG or rA:8-oxo-rG, the relative bypass frequency for rA:8-oxo-rG was found to be seven-fold higher than that for rC:8-oxo-rG. Therefore, the properties of RdRp indicated in this study may contribute to the mechanism of mutagenesis of the SARS-CoV-2 genome.