Endonuclease Activities in Extracts of Micrococcus Luteus that Act on γ-irradiated DNA

Author: Schön-bopp Annemarie   Schäfer Gisela   Hagen Ulrich  

Publisher: Informa Healthcare

ISSN: 1362-3095

Source: International Journal of Radiation Biology, Vol.31, Iss.3, 1977-03, pp. : 227-235

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Abstract

Several protein fractions containing endonuclease activity against γ-irradiated DNA (γ-endonuclease) were isolated from M. luteus. The crude extract was eluted on a phosphocellulose column and chromatographed on TEAE cellulose and subsequently on hydroxyapatite. Five peaks of γ-endonuclease were obtained from each preparation. Repeated experiments showed comparable chromatographic behaviour of the fractions. There was no detectable activity of U.V.-endonuclease in the fractions with γ-endonuclease but a small contamination of endonuclease against unirradiated DNA and against DNA with apurinic sites. The γ-endonuclease is stimulated by, but is not dependent on, magnesium. Several tests for endonuclease activity have been used: the analysis of strand breaks in calf-thymus DNA or in PM2 DNA, and the determination of end-groups formed by endonuclease, either 3′OH end-groups or phosphomonoester end groups. From the results obtained it can be assumed that the strand breaks induced by the γ-endonuclease carry 3′OH and 5′ phosphate end groups.