A form of DNA repair found in living cells in which damaged or mismatched bases in one of the two strands of DNA are cut out and replaced with the correct bases using the other strand as a template. It is performed by various enzymes. Typically, a DNA glycosylase enzyme recognizes the damage and excises the affected base. Then endonuclease enzymes nick the damaged strand either side of the site where the base was removed, allowing an exonuclease to remove the affected region of the strand. The gap is then repaired by a DNA polymerase, and the new section of the strand is rejoined to the existing strands by a DNA ligase. See also mismatch repair.