Mismatch repair of a nucleotide misincorporated by DNA polymerase. In E. coli, MutS2MutL2 binds a mismatch and scans the DNA for a GATC site. MutH nicks the DNA at the nearest unmethylated GATC site, facilitating repair of the mismatch on the newly synthesized strand by excision, filling in of the gap, and ligation.