[Peculiarities of 5-methylcytosine distribution in eukaryotic genome]

Most of it functions DNA methylation realizes as an integral part of the mechanism of remodeling and modification of chromatin structure. At the same time the global pattern of this complex reaction's net is still to be determined and we are just approaching to studying the mechanisms controlling epigenetic processes of histone modification and DNA methylation. Though cytosine methylation occurs predominantly at CpG sequences of eukaryotic genome, it also takes place at symmetric CpHpG and non-symmetric CpHpH sites (where H-A, T, or C). Various modification efficiency for these three site-specific DNA methylation types is observed depending on their genome localization. Different regions in eukaryotic genome are remarkable for their methylation features: CpG-islands, CpG-islands shores, differentially methylated regions of imprinted genes, and regions of non-alternative site-specific modification. Dependence of three canonical types (CpG, CpHpG, and CpHpH) of DNA methylation efficiency on their surrounding nucleotide context is noted. Existence of epigenetic code of DNA methylation, in which these context differences play specific functional role, has been supposed. The present review summarizes main up-to-date data on structural-functional features of site-specific cytosine methylation in eukaryotic genomes. Pathogenesis-related alterations of eukaryotic genome methylation pattern are considered as well.