MTase) is a member of a restriction-modification (R-M) system in Klebsiella pneumoniae and recognizes the sequence 5�-GGTACC-3�. It modifies the recognition sequence by transferring the methyl group from S-adenosyl-L-methionine (AdoMet) to the N 6 position of adenine residue. KpnI MTase occurs as a dimer in solution as shown by gel filtration and chemical crosslinking analysis. The nonlinear dependence of methylation activity on enzyme concentration indicates that the functionally active form of the enzyme is also a dimer. Product inhibition studies with KpnI MTase showed that S-adenosyl-L-homocysteine is a competitive inhibitor with respect to AdoMet and noncompetitive inhibitor with respect to DNA. The methylated DNA showed noncompetitive inhibition with respect to both DNA an
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