A SINGLE-STRANDED-DNA EXONUCLEASE FROM SCHIZOSACCHAROMYCES-POMBE

We have purified to near homogeneity a DNA exonuclease from meiotic cells of Schizosaccharomyces pombe. The enzyme, designated exonuclease II (ExoII), had an apparent molecular weight of 134 000 and was abundant in the cell. It specifically degraded single-stranded DNA in the 5'--> 3' direction with an apparent K(m) for 5' DNA ends of 3.6 X 10(-11) M and produced 5' deoxynucleoside monophosphates. Its mode of degradation is similar to that of the RecJ protein from Escherichia coli; ExoII may, therefore, be involved in genetic recombination and DNA damage repair.