SUMMARY: The transforming activity for an indole locus of DNA extracted from a methionine-requiring strain of was decreased about tenfold per unit of DNA by treatment of organisms with 0·025 -methylmethane-sulphonate for 30 min. at 37°. The treatment decreased the viable count to one tenth of the original and induced a reversion frequency of 10. Transforming activity of DNA prepared from alkylated organisms was sensitive, to heating at 50° as compared to DNA extracted from non-alkylated organisms. Methylation and heating of DNA did not inhibit its uptake by competent organisms. Incubation of treated and non-treated organisms in amino acid supplemented medium led to an increase in extractable transforming activity. A period of incubation which led to a 34% increase in DNA content more than doubled the transforming activity obtainable from methyl methanesulphonate treated organisms. The heat sensitivity of transforming DNA from alkylated organisms decreased after incubation of the organisms. Synthesis of DNA in the absence of a net DNA increase was demonstrated in methyl methanesulphonate treated organisms since thymidine-2-C was incorporated without lag from the start of incubation into an alkali-stable hot acid-soluble form. The experiments are interpreted to mean that alkylated DNA can serve as a template for the replication of DNA of normal activity.


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