Endonuclease Activities in Extracts ofMicrococcus Luteusthat Act on γ-irradiated DNA

Abstract

Several protein fractions containing endonuclease activity against .gamma.-irradiated DNA (.gamma.-endonuclease) were isolated from M. luteus. The crude extract was eluted on a phosphocellulose column and chromatographed on TEAE cellulose and subsequently on hydroxyapatite. Peaks (5) of .gamma.-endonuclease were obtained from each preparation. Repeated experiments showed comparable chromatographic behavior of the fractions. There was no detectable activity of UV-endonuclease in the fractions with .gamma.-endonuclease but a small contamination of endonuclease against unirradiated DNA and against DNA with apurinic sites. The .gamma.-endonuclease is stimulated by, but is not dependent on, Mg. Several tests for endonuclease activity were used: the analysis of strand breaks in calf-thymus DNA or in [phage] PM2 DNA, and the determination of end-groups formed by endonuclease, either 3''OH end-groups or phosphomonoester end groups. The strand breaks induced by the .gamma.-endonuclease apparently carry 3''-OH and 5'' phosphate end groups.