Abstract
Chemical modifications of chosen amino acid residues: arginine, histidine, cysteine, glycine and tryptophan have been attempted to investigate their role in catalysis and DNA binding by MspI DNA methyltransferase (M.MspI). The catalytic inactivation following modifications of two arginine and three histidine moieties was a consequence of loss of DNA binding property of the methyltransferase. Modification of a single cysteine residue completely abolished the ability of M.MspI to transfer a methyl group but there was no loss of DNA binding activity. While tryptophan had no apparent functional role, glycine was critical for AdoMet binding and target base methylation by the M.MspI.