Purification and properties of a single strand-specific endonuclease from mouse cell mitochondria

A nuclease was purified from mitochondria of the mouse plasmacytoma cell line, MCP-11 which acts on single-stranded DNA endonucleolytically and appears to have no activity upon native DNA. It degrades unordered RNA somewhat more effectively than it does DNA. The enzyme activity and the major detectable polypeptide migrate to a position corresponding to an Mr of 37,400 on denaturing polyacrylamide gels; in its native form the activity has an S value of 4.7, which corresponds to a molecular weight of roughly 73,000. The single-strand DNase activity has a pH optimum near 7.5, requires a divalent cation and is inhibited by EDTA, phosphate, KCl and NaCl. The enzyme is remarkably similar to fungal mitochondrial enzymes whose absence in various mutants correlates with defective DNA repair and recombination. It reacts weakly with antibody to a form of such an enzyme from Neurospora crassa.