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 $PDX_n(D/E)XK$ 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