The domain structure and the function of poly(ADP-ribose) synthetase

Abstract

Poly(ADP-ribose) synthetase is a chromatin-bound enzyme which synthesizes a protein-bound homopolymer of ADP-ribose utilizing NAD as a substrate. The characteristic nature of this enzyme is that it requires DNA for catalytic activity. The enzyme is rich in malignant tumor cells as well as in normal tissues where cell proliferation is very rapid. The enzyme has been purified to homogeneity from calf thymus, mouse testis and human placenta. The amino acid composition of these enzymes is very similar and a monoclonal antibody as well as antisera against the calf enzyme cross-reacts with mouse, chicken and human enzymes, suggesting that the antigenic structures of poly(ADP-ribose) synthetase are highly conserved in various animal cells. The native enzyme (Mr = 120K) is cleaved by limited proteolytic digestion into three different domains (Mr = 46K, 22K, 54K), the first containing the site for DNA binding, the second containing the site for automodification and the third containing the site for NAD binding. The DNA binding domain (Mr = 46K), like the native enzyme, has the ability to preferentially suppress nick induced random transcription initiation in a HeLa cell lysate, resulting in the production of run-off RNA initiated from the correct late promoter site on truncated DNA of adenovirus 2. The native enzyme poly(ADP-ribosyl)ates RNA polymerase and some other nuclear enzymes. These results, taken together, indicate that poly(ADP-ribose) synthetase plays a critical role in regulating gene expression in various eukaryotic cells.