They catalyzes the transfer of methyl group from donor to DNA.
They are part of Restriction modification system
Type-II methylases are encoded by separate proteins whereas in Type-I and III same protein complex performs both restriction and modification activities. S Adenosyl Methionine (SAM) donates the methyl group for methylation
1. Dam Methylase- methylates the amino group at C-6 position of Adenine and frequency is 256 bp residue in GATC.These Methylases present in all Restriction Modification systems (RM) (I ,II, III).

2. Dcm Methylase – Methylation of amino group at the C-4 position of Cytosines of CCAGG, CCTGG and one site for every 512 bp. Dcm methylases are components of type-II RM system

Biological function of methylase is to protect host DNA from its own restriction endonucleases

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