Effects of Methylation on the Activities of Restriction Enzymes

Many DNA molecules contain methylated bases. When restriction enzyme recognition enzymes are methylated, DNA digestion at that site may be blocked depending on the enzyme and the type of methylation that has occurred. Most strains of E. coli have two site-specific DNA methylases (also known as methyltransferases), dam methylase (G6mATC) and dcm methylase (C5mCWGG), and DNA molecules prepared from dam+ dcm+ E. coli strains are methylated at each site. Some mammalian DNA molecules are methylated by CG methylase (5mCG). Information about restriction enzymes whose activities are affected by dam methylase, dcm methylase, or CG methylase, as well as the sequences recognized by each methylase, are listed below. Refer to the footnotes below the table for additional details.

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