DNA Methyltransferase

DNA methylation, defined by the addition of a methyl group to adenine or cytosine bases in DNA catalyzed by DNA methyltransferases (MTases), is one of the most studied post-replicative DNA modification mechanism in bacteria. The three forms of nucleotide methylation identified to date are: N6-methyladenine(^m6A), N4-methylcytosine (^m4C), and 5-methylcytosine (^m5C).

DNA methylation, one type of epigenetic modification, represses gene expression. DNA methylation is caused primarily by a family of DNA methyltransferases (DNMTs) including DNMT1, DNMT3a and DNMT3b. Conventionally, DNMT1 acts as the primary maintenance methyltransferase to keep the methylation of DNA that is already established at the genome, whereas DNMT3a and DNMT3b are classified asde novo methyltransferases to reversibly methylate unmethylated DNA. DNA methylation represses gene transcription through several mechanisms including physically blocking the binding of transcription factors and/or functioning as docking sites for transcriptional repressors/corepressors.

In epigenetic transcriptional regulation, which is important for embryonic development, DNA-methylation patterns are determined by de novo methylation by the DNA methyltransferases Dnmt3a and Dnmt3b in the embryo.

DNA methylation on the cytosine of CpGdinucleotides in gene promoter regions is associated with silencing gene expression. Of the DNA methyltransferases, only DNA methyltransferase 3a (DNMT3a) and 3b (DNMT3b) are capable of adding de novo CpG methylation marks and thus may dynamically regulate gene silencing.