Protein involved in the repair of damages to one strand of DNA (loss of purines due to thermal fluctuations, formation of pyrimidine dimers by UV irradiation, for instance). The site of damage is recognized, excised by an endonuclease, the correct sequence is copied from the complementary strand by a polymerase and the ends of this correct sequence are joined to the rest of the strand by a ligase. In bacterial systems, the polymerase also acts as endonuclease. Excisase A and other proteins involved in recombination mediate DNA excision; a process whereby abnormal or mismatched nucleotides are enzymatically cut out of a strand of a DNA molecule.