Fig. 7. The NER-dependent H2AX phosphorylation coincides with 53BP1 accumulation at damaged sites but not with Chk1 Ser345 phosphorylation. (A) MSU-2 cells (AS or G0) were exposed to 20 J/m2 UV and incubated for 2 or 4 hours. Cell lysates were prepared with SDS sample buffer (Bio-Rad) and analyzed by immunoblotting with the specific antibodies as indicated. (B) MSU-2 or XP1CTA cells under growth-arrested conditions were locally irradiated with 20 J/m2 UV and stained with anti-53BP1 antibody after 4 hours of incubation. (C) Growth-arrested MSU-2 cells were locally irradiated with 10 J/m2 UV, incubated for 1 hour in the presence or absence of Ara-C and stained with anti-53BP1 antibody.