Poly(ADP-ribosyl)ation of chromosomal proteins in the HeLa S3 cell cycle

Change in the level of poly(ADP-ribosyl)ation during the cell cycle of HeLa S3 cells was examined in three different in vitro systems: isolated nuclei, chromatin, and poly(ADP-ribose) polymerase extracted from isolated nuclei, and by the direct immunofluorescent antibody technique in situ. In isolated nuclei, after release from thymidine-hydroxyurea double block, the level of poly(ADP-ribosyl)ation was low in the S phase and increased in the late G2 phase with a peak in the M phase. In chromatin, the level began to increase in the mid-late S phase, was maintained at a high level throughout the G2 phase, decreased in the M phase, and became basal during the G1 phase. The activity of poly(ADP-ribose) polymerase extracted from isolated nuclei was relatively high throughout the cell cycle and was highest in the G2 phase. Similar changes during the HeLa S3 cell cycle were observed in the three systems after release from Colcemid block. In synchronously growing HeLa S3 cells in situ, nuclei in the G2-M phase were stained strongest for poly(ADP-ribose) by the immunofluorescent staining. These results were consistent with the peak of poly(ADP-ribosyl)ation in the G2-M phase observed in the nuclear system in vitro.