Effect of interaction between 5-azacytidine and DNA (cytosine-5) methyltransferase on C-to-G and C-to-T mutations in Escherichia coli.

The purpose of this study was to determine the effect of the Dcm cytosine methyltransferase on 5-azacytidine (5-azaC) mutagenesis in Escherichia coli. We used a Lac reversion assay to measure C-to-G and C-to-T mutations at a single, methylatable cytosine in the lacZ gene, in the presence and absence of Dcm. C-to-G mutations are stimulated by 5-azaC but are largely independent of Dcm. In contrast, C-to-T mutations are not stimulated by 5-azaC in either wild type or dcm cells. However, in cells which contain Dcm but are defective in very short patch repair, the normally high frequency of spontaneous C-to-T mutations is decreased by the analog in a dose-dependent manner.