Poly(ADP-ribose) synthetase. The DNA binding domain and the automodification domain

Poly(ADP-ribose) synthetase is known to require double-stranded DNA for activity and to be susceptible to automodification with poly(ADP-ribose). This enzyme is cleaved into two fragments by limited proteolysis with papain. Their molecular weights are 74,000 and 46,000, respectively, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The fragment of Mr 46,000 binds to a nicked DNA-cellulose column with the same affinity as that of native enzyme, while the fragment of Mr 74,000 has little affinity for the DNA ligand. When the enzyme previously automodified with [adenine-U-14C]NAD (2 ADP-ribose units incorporated per molecule of enzyme) is digested with papain, the label is detected only in the fragment of Mr 74,000. These results indicate that poly(ADP-ribose) synthetase contains two domains, one acting as the site for binding of DNA and the other acting as the site(s) for accepting poly(ADP-ribose).