I'm working on a piece of software that computes melting temperatures for nucleic acid duplexes, and I'm about to add support for 5-methylcytosine as a nucleotide base. At the moment, the bases accepted by the program are adenine, cytosine, guanine, thymine and uracil, with their standard letters A,C,G,T,U. Is there a standard letter for 5-methylcytosine? The only example I've found is this paper, which uses an italic C for 5mc, but I want a distinct letter. The three candidates I've thought of are:
- 5 - for '5-methylcytosine'
- M - for 'methyl'
- B - Since methylation of U gives you T, which is one place earlier in the alphabet, so methylation of C gives B.