5-methylcytosine, commonly abbreviated as "mC", is a chemical modification first identified in tRNA. Since its initial identification, 5-methylcytosine has been found in a variety of different cellular structures ranging from a variety of RNAs and even DNA. Two different kinds of RNA mC "writers" have been identified: NOP2/SUN RNA methyltransferase (NSUN) and DNA methyltransferase-2. It is important to note that DNMT-2 is a protein that falls under the DNMT family, which contains three other DNMTs (1, 3a, and 3b) known to demonstrate methylation activity in relation to the genome. Uniquely, DNMT-2 is the only DNMT that has been confirmed to methylate both DNA and RNA, although its overall DNA methylation function is significantly less than that of its counterparts. While these writers have been identified, as of now, there are no known mC "erasers"; in a broader sense, this means that reamination, or the conversion of 5-methylcytosine back into cytosine, has not been observed in RNA. 5-methylcytosine modifications are typically found approximately 100 nucleotides downstream of translation initiation sites. This may provide some insight into the purpose of these modifications; for instance, this may indicate that these modifications are important for controlling the fate of the RNA, such as whether it will be translated or not in the case of mRNA. However, the exact purpose of the methylation at specific cytosines in RNA is currently unknown. One possibility may be that mC may be associated with RNA transport, since the Aly/REF export factor is a known mC binding protein. On the other hand, mC modifications could possibly be associated with the regulation of genes involved in energy and lipid metabolism, through modulation of the overall RNA translational fate.