5-Methylcytosine in genes with methylation-dependent regulation

An asymmetric distribution of deoxy-5-methylcytidylic acid-inhibiting restriction sites (dcm-sites) takes place in ten human genes regulated by 5-methylcytosine. These genes are dcm-site enriched upstream and dcm-site poor downstream. Along them, there is a scattering of hypermethylatable introns and hypomethylatable exons with a common code: the 5mCpG dinucleotides characterize promoters; Gp5mCs characterize introns; Tp5mCs and Cp5mCs are in small concentrations in exons. Housekeeping genes contain more dcm-sites when compared with tissue-specific genes. This depends on the higher number of dcm-sites in their promoters and introns. In exons, the relatively lower number of dcm-sites is almost the same in both housekeeping and tissue-specific genes. Going from 5' to 3', the average frequency of occurrence of these sites per nucleotide units decreases in introns and increases in exons. This difference is highly discriminated for tissue-specific and less discriminated for housekeeping genes.