Epitranscriptomic m 5 C methylation of SARS-CoV-2 RNA regulates viral replication and the virulence of progeny viruses in the new infection.

While the significance of N6-methyladenosine (m 6 A) in viral regulation has been extensively studied, the functions of 5-methylcytosine (m 5 C) modification in viral biology remain largely unexplored. In this study, we demonstrate that m 5 C is more abundant than m 6 A in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and provide a comprehensive profile of the m 5 C landscape of SARS-CoV-2 RNA. Knockout of NSUN2 reduces m 5 C levels in SARS-CoV-2 virion RNA and enhances viral replication. Nsun2 deficiency mice exhibited higher viral burden and more severe lung tissue damages. Combined RNA-Bis-seq and m 5 C-MeRIP-seq identified the NSUN2-dependent m 5 C-methylated cytosines across the positive-sense genomic RNA of SARS-CoV-2, and the mutations of these cytosines enhance RNA stability. The progeny SARS-CoV-2 virions from Nsun2 deficiency mice with low levels of m 5 C modification exhibited a stronger replication ability. Overall, our findings uncover the vital role played by NSUN2-mediated m 5 C modification during SARS-CoV-2 replication and propose a host antiviral strategy via epitranscriptomic addition of m 5 C methylation to SARS-CoV-2 RNA.