Methylation of deoxyribonucleic acid by diazomethane

Abstract

1. 1. Aqueous solutions of salmon-sperm DNA were treated with diazomethane and diazoethane dissolved in ether. In both cases 7-alkylguanines and 3-alkyladinines were formed in a ratio of 3–4:1. The yields of the ethylated purines were much smaller than those of the methylated purines. The ethylating capacity appeared to be inversely related to the rate of protonation of diazoethane. Per 100 deoxynucleotides about 16 phosphate groups were esterified and 6 purines were methylated by diazomethane. 2. 2. Incubation of DNA with methylamine plus nitrous acid at pH 4 led also to the formation of 7-methylguanine. 3. 3. The hyperchromicity was fully retained in methylated DNA, but the slope of the absorbancy-temperature curve suggested that the change in the secondary structure (unfolding) was preceded by one in the primary structure of methylated DNA during heating. The latter change (main chain fission) may be triggered off by the loss of methylated purines, 3-methyladenine being released 4–5 times faster than 7-methylguanine at pH 7.4 and 37°. 4. 4. The differences in reaction between DNA and RNA with diazomethane are described.