A Mutation in the Mod Subunit of EcoP15I Restriction Enzyme Converts the DNA Methyltransferase to a Site-specific Endonuclease

Abstract A closer inspection of the amino acid sequence of EcoP15I DNA methyltransferase revealed a region of similarity to the PDXn(D/E)XK catalytic site of type II restriction endonucleases, except for methionine in EcoP15I DNA methyltransferase instead of proline. Substitution of methionine at position 357 by proline converts EcoP15I DNA methyltransferase to a site-specific endonuclease. EcoP15I-M357P DNA methyltransferase specifically binds to the recognition sequence 5′-CAGCAG-3′ and cleaves DNA asymmetrically EcoP151-M357P·DNA methyltransferase specifically binds to the recognition sequence 5′-CAGCAG-3′ and cleaves DNA asymmetrically, 5′-CAGCAG(N)10-3′, as indicated by the arrows, in presence of magnesium ions.