5-Methylcytosine profiles in mouse transcriptomes suggest the randomness of m 5 C formation catalyzed by RNA methyltransferase

Objective 5-Methylcytosine (m 5 C) is a type of chemical modification on the nucleotides and is widespread in both DNA and RNA. Although the DNA m 5 C has been extensively studied over the past years, the distribution and biological function of RNA m 5 C still remain to be elucidated. Here, I explored the profiles of RNA m 5 C in four mouse tissues by applying a RNA cytosine methylation data analysis tool to public mouse RNA m 5 C data. Results I found that the methylation rates of cytosine were the same with the averages of methylation level at single-nucleotide level. Furthermore, I gave a mathematical formula to describe the observed relationship and analyzed it deeply. The sufficient necessary condition for the given formula suggests that the methylation levels at most m 5 C sites are the same in four mouse tissues. Therefore, I proposed a hypothesis that the m 5 C formation catalyzed by RNA methyltransferase is random and with the same probability at most m 5 C sites, which is the methylation rate of cytosine. My hypothesis can be used to explain the observed profiles of RNA m 5 C in four mouse tissues and will be benefit to future studies of the distribution and biological function of RNA m 5 C in mammals.