For example, exonuclease 1 (EXO1) has been reported to carry out excision of nucleotides in the 5′- > 3′ direction.263 Another protein, replication protein A (RPA) serves as a binding function of single-strand DNA produced by EXO1 to prevent further DNA degradation.264 MLH1, a subunit of MutLα, whose defect is responsible for ~50% of MMR defected cancers, may restrained DNA excessive excision by EXO1.265 Immediately following the recognition step, the removal step occurs. The gene discussed is EXO1; the disease is cancer.