The Enzymatic Methylation of Ribonucleic Acid and Deoxyribonucleic Acid. v. Purification and Properties of the Deoxyribonucleic Acid-methylating Activity of Escherichia Coli.

The classical investigations of Wyatt (2) and Dunn and Smith (3) established the existence of 5-methylcytosine and 6-methylaminopurine as constituents of the deoxyribonucleic acid of higher plants and animals, and of bacteria and bacterial viruses, respectively. Until recently, the biochemical pathways for the incorporation of these “trace bases” into deoxyribonucleic acid was unknown although it had been shown that the deoxyribonucleoside triphosphate of 5-methylcytosine could quantitatively replace deoxycytidine triphosphate as a substrate for the enzyme deoxyribonucleic acid polymerase (4). The discovery that the glucosylation of the DNA of the T-even bacteriophages (5) and methylation of soluble ribonucleic acid (6) occurred at the polynucleotide level suggested that the incorporation of methyl groups might also take place after polymerization in the biosynthesis of DNA. In previous communications from this laboratory, the presence of an enzyme activity in Escherichia coli which catalyzes the transfer of methyl groups to cytosine and adenine moieties of a variety of DNAs has been reported (7-9). This reaction can be represented by the following equation.