hMSH2-independent DNA mismatch recognition by human proteins

Two distinct mismatch binding activities are detected using bandshift assays with human cell extracts and DNA with mispairs at defined positions. One requires hMSH2 protein and is absent from extracts of LoVo cells, which contain a partial deletion of the hMSH2 gene. The second activity is independent of hMSH2 and is present at normal levels in LoVo and three other cell lines, which are defective in in vitro hMSH2-dependent binding. The two mismatch recognition activities are distinguished by their sensitivity to polycations and can be resolved by chromatography on MonoQ. hMSH2-independent activity has been purified extensively from wild-type cells and from a cell line deficient in hMSH2-dependent binding. The purified material preferentially recognizes A-C, some pyrimidine-pyrimidine mismatches, and certain slipped mispaired structures. Binding exhibits some sequence preferences. The similar properties of the two mismatch binding activities suggest that they both contribute to mismatch repair.