SELF-METHYLATION OF BSPRI DNA-METHYLTRANSFERASE

The DNA (cytosine-5)-methyltransferase (m5C-MTase) M.BspRI is able to accept the methyl group from the methyl donor S-adenosyl-L-methionine (AdoMet) in the absence of DNA. Transfer of the methyl group to the en zyme is a slow reaction relative to DNA methylation. Self-methylation is dependent on the native conformation of the enzyme and is inhibited by S-adenosyl-L-homocysteine, DNA and sulfhydryl reagents. Amino acid sequencing of proteolytic peptides obtained from M.BspRI, which had b een methylated with [methyl-H-3] AdoMet, and thin layer chromatography of the modified amino acid identified two cysteines, Cys156 and Cys18 1 that bind the methyl group in form of S-methylcysteine. One of the a cceptor residues, Cys156 is the highly conserved cysteine which plays the role of the catalytic nucleophile of m5C-MTases.