IN-VITRO PROTEOLYSIS OF ENDONUCLEASES IN RAT-LIVER NUCLEI EXTRACTS

DNA endonucleases in rat liver nuclei extracts were examined by SDS-po lyacrylamide gel electrophoresis followed by zymogram analysis. Four p olypeptides of 120, 54, 31 and 28 kDa, which have DNA endonuclease act ivity, were shown to occur in the extract isolated in the presence of phenylmethanesulfonyl fluoride (PMSF), a proteinase inhibitor. Isolati on without PMSF, as well as storage at -20 degrees C, or autodigestion , resulted in multiplication of active polypeptides in the extracts. T rypsin digestion led to the appearance of an active >140 kDa polypepti de, indicating the existence of a potential endonuclease precursor in the nuclear extract.