Mismatch repair in mammalian cells.

A vital process in maintaining a low genetic error rate is the removal of mismatched bases in DNA. The importance of this process in E. coli is demonstrated by the 100-1000 fold increase in mutation frequency observed in cells deficient in this repair system. Mismatches can arise as a consequence of recombination, errors in replication and as a result of spontaneous chemical deamination, the latter process resulting in an estimated twelve T:G mismatches per genome per day in mammalian cells. Recent studies, discussed here, provide evidence for the existence of specific mismatch repair systems in mammalian and human cells.