Mismatch repair of deaminated 5-methyl-cytosine.

Deamination of 5-methyl-cytosine in double-stranded DNA produces a G-T mismatch. Heteroduplexes of bacteriophage lambda DNA containing a G-T mismatch at the site of a G-5-meC base-pair in one of the parental phages were constructed and used to transfect Escherichia coli cells. Genetic analysis of the progeny phages derived from such heteroduplexes suggests that, in E. coli, mismatches resulting from the deamination of 5-methyl-cytosine are repaired by a system requiring the E. coli dcm methylase and some, but not all, of the functions of the E. coli methyl-directed mismatch repair system. The repair appears to act only on the G-T mismatch and acts specifically to restore the cytosine methylation sequence.