On heterogeneity of DNA methylases from Escherichia coli SK cells.

The presence of E. coli SK cells of five different DNA-methylases differing in specificity to the methylated sequence is documented has been proven. Two enzymes methylate cytosine with the formation of 5'-methylcytosine and three enzymes methylate adenine with formation of 6'-methylaminopurine. A method for simultaneous isolation of the five individual enzymes including gel filtration on Biogel A-0.5 M is proposed. The direct evidence has been presented showing that the additional methylation test in our method modification actually can discriminate between enzymes differing in sensitive sites.