In vitro methylation of DNA by the fumigant methyl bromide.

Investigations have shown that the physical state of the DNA strongly influences the pattern of methylation observed when DNA or a substance containing DNA is treated with the fumigant methyl bromide. 1-Methyl-adenine and 7-methylguanine were identified, after hydrolysis, as the major methylated bases of DNA which had been treated in the solid state. 3-Methylcytosine, 3-methyladenine and 7-methyladenine were found as minor products. The overall methylation pattern was similar to that observed earlier for DNA of maize and wheat which had been fumigated. In contrast, when buffer solutions of DNA were treated with methyl bromide, the N-7 position of guanine was the major site and the N-3 position of adenine was the second most important site of methylation. This result corresponds to that previously observed in similar studies with buffer solutions of DNA and other methylating agents.