Poly(ADP-ribose) and differentiation of Friend Erythroleukemia cells. Restriction of the chain lenght.

1. Poly(ADP-ribose) synthesized in nuclei isolated from Friend erythroleukemic cells was characterized. Although the activity of poly(ADP-ribose) synthesis of cells induced to differentiate was suppressed to about one-third of that of uninduced cells, the chain length were identical, and were clearly restricted within a narrow band in polyacrylamide gels, moving at about half the speed of bromphenol blue. 2. The restriction of chain length was also observed in rat liver nuclei, though some poly(ADP-ribose) chains could be degraded into smaller pieces during incubation. Treatment of nuclei with a high concentration of detergent and sonication before incubation caused aberrant synthesis of poly(ADP-ribose) chains which were not restricted in size. 3. In contrast, the average chain length of the 3H-labeled portion of poly(ADP-ribose) synthesized during incubation of nuclei with 3H-NAD+ was found to be reduced to 50% of that in the induced cells. 4. Under our reaction conditions, about 95% of newly synthesized poly(ADP-ribose) was linked to non-histone nuclear proteins. The total content of the non-histones was reduced to about 50% by treatment with inducers. 5. In view of the above findings, it is suggested that the decrease of chain initiation frequency caused by the partial loss of available acceptor sites may be correlated with the suppression of poly(ADP-ribose) synthesis in induced cells.