No evidence for epitranscriptomic m 5 C modification of SARS-CoV-2, HIV and MLV viral RNA.

The addition of chemical groups to cellular RNA to modulate RNA fate and/or function is summarized under the term epitranscriptomic modification. More than 170 different modifications have been identified on cellular RNA, such as tRNA, rRNA and, to a lesser extent, on other RNA types. Recently, epitranscriptomic modification of viral RNA has received considerable attention as a possible additional mechanism regulating virus infection and replication. N6-methyladenosine (m 6 A) and C5-methylcytosine (m 5 C) have been most broadly studied in different RNA viruses. Various studies, however, reported varying results with regard to number and extent of the modification. Here we investigated the m 5 C methylome of SARS-CoV-2, and we re-examined reported m 5 C sites in HIV and MLV. Using a rigorous bisulfite-sequencing protocol and stringent data analysis, we found no evidence for the presence of m 5 C in these viruses. The data emphasize the necessity for optimizing experimental conditions and bioinformatic data analysis.