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Methylase

(Methylase, Methyltransferase, MTase)

Enzyme in the restriction-modification system of bacteria that transfer methyl group (or hydroxymethyl) to cytosine or adenine. TypeII methylases are usually used for construction or cloning.

M.EcoRI
RecognitionMethylated

Adenines are methylated by M.EcoRI in this example.

Sometimes methyl groups on the DNA prevent from digestion by restriction enzyme. Since bacteria used for cloning often dam methylase and dcm methylase, it is neccessary to pay attention to the methylated sites.