Epitranscriptomic Addition of m5C to HIV-1 Transcripts Regulates Viral Gene Expression.

Abstract

How the covalent modification of mRNA ribonucleotides, termed epitranscriptomic modifications, alters\xa0mRNA function remains unclear. One issue has been the difficulty of quantifying these modifications. Using purified HIV-1 genomic RNA, we show that\xa0this RNA bears more epitranscriptomic modifications than the average cellular mRNA, with 5-methylcytosine (m5C) and 2 O-methyl modifications being\xa0particularly prevalent. The methyltransferase NSUN2 serves as the primary writer for m5C on HIV-1 RNAs. NSUN2 inactivation inhibits not only m5C addition to HIV-1 transcripts but also viral replication. This inhibition results from reduced HIV-1 protein, but not mRNA, expression, which in turn correlates with reduced ribosome binding to viral mRNAs. In addition, loss of m5C dysregulates the alternative splicing of viral RNAs. These data identify m5C as a post-transcriptional regulator of both splicing and function of HIV-1 mRNA, thereby affecting directly viral gene expression.