Repair of single nucleotide DNA mismatches transfected into mammalian cells can occur by short-patch excision.

Synthetic DNA linkers containing a single mismatched nucleotide (C:A) are repaired without bias at high efficiency when introduced into mammalian cells on a SV40 shuttle vector. From the pattern of repair in vectors containing multiple linkers, it appears that DNA synthesis following mismatch excision can replace a length of DNA as short as 40 nucleotides. Furthermore, results from the introduction of linker molecules containing combinations of single-strand nicks suggest that transient unsealed nicks do not drive the direction of mismatch repair in mammalian cells, as has previously been proposed.