DNA Methyltransferase

DNA methyltransferases, also termed DNA MTase, consist of an enzyme family that catalyzes the transfer of methyl groups to DNA, in the process of DNA methylation. The methyl donor group utilized is an S-adenosyl methionine.

There are four DNA methyltransferases in mammals.

DNMT1, DNMT2, DNMT3A and DNMT3B.

DNMT1

DNMT1 is the most important and most common DNA methytransferase. DNMT1 is 1620 amino acids in length, with a regulatory domain found within the first 1000 amino acids. The remaining amino acid residues act as the catalytic domain. Both regions are essential for DNMT1 function.

DNMT1 Function

DNMT1 methylates hemimethylated CpG dinucleotides within the genome of mammals. Critical, is the fact that DNMT1 activity is high on hemimethylated DNA versus unmethylated DNA.

DNMT1 Isoforms

DNMT1 isoforms include somatic DNMT1, a splice variant termed DNMT1b found wihtin the nucleus of somatic cells, and an isoform termed DNMT1o specific for oocytes and crucial for the development of the embryo.

DNMT2

DNMT2 does not methylate DNA, but methylate aspartic acid within transfer RNA, tRNA. It is therefore termed TRDMT1, as tRNA aspartic acid methyltransferase 1. It does however, have homology and similarities to 5-methylcytosine methyltransferases.
 

DNMT3

DNMT3 consists of DNMT3a, DNMT3b and DNMT3L. These enzymes are similar to DNMT1, both in sequence and structure. The major difference is that DNMT3 methylates DNA at the same rate whether it is hemimethylated or unmethylated.