DNA cytosine methylation and heat-induced deamination

Abstract
The heat-induced conversion of 5-methylcytosine (m5C) residues to thymidine residues and of cytosine to uracil residues in single-stranded DNA was studied. The calculated rates for deamination at 37.degree. C and pH 7.4 were .apprx. 9.5 .times. 10-10 and 2.1 .times. 10-10 sec-1, respectively. N4-Methyldeoxycytidine, which is in the DNA of certain thermophilic bacteria, was more heat-resistant than was deoxycytidine and much more than was 5-methyldeoxycytidine. Thermophilic bacteria which contain N4-methylcytosine rather than m5C in their genomes may thereby largely avoid heat-induced mutation due to deamination, which is incurred by the many organisms that contain m5C in their DNA.

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