Yeast Redoxyendonuclease, a DNA Repair Enzyme Similar to Escherichia coli Endonuclease III

A DNA repair endonuclease (redoxyendonuclease) was isolated from bakers′ yeast (Saccha-romyces cerevisiae). The enzyme has been purified by a series of column chromatography steps and cleaves OsO₄-damaged, double-stranded DNA at sites of thymine glycol and heavily UV-irradiated DNA at sites of cytosine, thymine, and guanine photoproducts. The base specificity and mechanism of phosphodiester bond cleavage for the yeast redoxyendonuclease appear to be identical with those of Escherichia coli endonuclease III when thymine glycol containing, end-labeled DNA fragments of defined sequence are employed as substrates. Yeast redoxyendonuclease has an apparent molecular size of 38 000–42000 daltons and is active in the absence of divalent metal cations. The identification of such an enzyme in yeast may be of value in the elucidation of the biochemical basis for radiation sensitivity in certain yeast mutants.