IN VITRO INHIBITION OF HELA CELL NUCLEAR RIBONUCLEASES BY ADP-RIBOSYLATION

Ribonuclease activity in HeLa cell nuclei is markedly inhibited by ADP-ribosylation following incubation of intact isolated nuclei with [14C]NAD. Time course experiments demonstrate that [14C] incorporation into proteins is accompanied by a 50% inhibition of ribonuclease activity on single-strand and double-strand polynucleotides. Inhibition does not occur when 3-aminobenzamide, a potent (ADP-ribose) polymerase inhibitor, is present. Two enzymatic activities that degrade double-strand polynucleotides have been purified and partially characterized. A relevant level of radioactivity resulting from [14C]NAD incubation of nuclei was associated to the purified enzyme. The RNase F1 component, which shows maximal activity on polyU-polyA is demonstrated to be the major ADP-ribose acceptor protein.