EFFECT OF 5-AZACYTIDINE ON ESCHERICHIA-COLI DNA METHYLASE

5-Azacytidine, when added to growing E.coli K12, causes a decrease in DNA methylation assayed invitro. This decrease is greater when E.coli DNA is used as substrate than when calf thymus DNA is used. The decrease in activity is not due to the inhibition of protein synthesis caused by this drug, since neither chloramphenicol nor rifampin causes a decrease in enzyme activity. The effect is specific for the DNA(cytosine-5)methylase; the methylation of adenine is not affected. The concentration of drug that inhibits the DNA methylase by 50% is the same concentration that inhibits cell growth by 50%. © 1979.