FIG. 4.

In vivo negative regulation of PARP activity by XRCC1. HeLa cells expressing either GST alone (A to C) or GST-XRCC1 (D to F) were treated with H₂O₂ for 10 min. After methanol-acetone fixation, the cells were incubated with a mixture of monoclonal antibodies against GST and against poly(ADP-ribose) (pADPr). The primary antibodies were detected with Texas red or fluorescein isothiocyanate-conjugated secondary antibodies. Arrowheads point out cells expressing GST-XRCC1 and lacking PARP activity (D to F). DAPI, 4′,6-diamidino-2-phenylindole.