Mismatch correction catalyzed by cell-free extracts of Saccharomyces cerevisiae.

Heteroduplex DNA substrates containing a 4- or 7-base-pair insertion/deletion mismatch or each of the eight possible single-base-pair mismatches were constructed. Extracts of mitotic Saccharomyces cerevisiae cells catalyzed the correction of mismatched nucleotides in a reaction that required Mg2+ and had a partial requirement for ATP and the four dNTPs. The insertion/deletion mismatches and the A X C and G X T mismatches were repaired efficiently, while the six other single-base-pair mismatches were repaired poorly or at undetectable rates. Mismatch correction was accompanied by the specific incorporation of less than 20 nucleotides at or near the site of the repaired mismatch.