DNA methyltransferase n a methyltransferase that promotes the covalent addition of a methyl group to a specific nucleotide base in a molecule of DNA
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DNA meth·yl·trans·fer·ase (meth″əl-transґfər-ās) any of a group of enzymes that catalyze the transfer of a methyl group from S-adenosylmethionine to a specific nucleotide in a DNA molecule, with different enzymes specific for nucleotide and position of methylation. In eukaryotes, the methylated base is virtually always cytosine methylated at the C5 position, and the reaction is catalyzed by the methyltransferase officially called DNA (cytosine-5-)-methyltransferase. Different organisms have different methylation recognition sequences; in animal cells, methylation occurs specifically at 5′-CG-3′ sequences, and methylation is involved in gene expression. There are two types of DNA methyltransferases: those methylating unmethylated DNA, called de novo methyltransferases, and those that methylate the unmethylated strand of DNA produced upon replication of methylated DNA, called maintenance methyltransferases. See also DNA methylation, under methylation.Medical dictionary. 2011.