Poly(ADP-ribose): release of template restriction in HeLa cells

Evidence is presented to show that ADP-ribosylation of nuclear proteins by poly(ADP-ribose) polymerase enhances template-primer activity of HeLa cell nuclear DNA. We used Escherichia coli DNA polymerase I (EC 2.7.7.7; DNA nucleotidyltransferase) as an exogenous probe of nuclear DNA status. Neither NAD nor free poly(ADP-ribose) acts directly on the bacterial enzyme. The stimulation is specific for formation of ADP-ribosylated proteins and is not a generalized polyanion or nucleotide effect on chromatin. The release of template restriction is proportional to the capacity of a given cell line to synthesize poly(ADP-ribose); both the stimulation and poly(ADP-ribose) formation are coordinately proportional to NAD concentration. Binding studies with DNA polymerase indicate exposure or generation of additional 3'-OH primer sites due to ADP-ribosylation in intact nuclei. With intact cells, there appears a correlation among growth, physiological template restriction, and the above effects of ADP-ribosylation.