Fig. 2.

Co-activation of the histone H4/n gene by HiNF-P and p220^NPAT occurs independently of γirradiation. U2OS cells were transiently transfected with a wild-type histone H4 promoter luciferase reporter construct and co-transfected with the expression vectors for HiNF-P (P), or p220^NPAT (N), or empty expression vector (EV). For irradiation experiments, cells were exposed to 5 Gy at 24 h after transfection. At 4 or 16 h after irradiation, cell lysates were analyzed for (A) protein levels of HiNF-P and p21^CIP1/WAF1 by western blotting protein and (B, C) for luciferase activity. Firefly (FF) luciferase activity was normalized to Renilla (RL) luciferase activity in panel B. In panel C, these values are normalized to the empty vector. Error bars indicate standard deviations from triplicate experiments.