Fig. 9. p21 does not inhibit UDS repair activity. (A) Untreated or TSA-treated LF1 fibroblasts were irradiated with UV-C (10 J/m²), and incubated with 100 µM BrdU for 3 hours. Cells were then fixed and immunostained with anti-BrdU antibody, a secondary biotinylated antibody followed by streptavidin-FITC. Fluorescence images of untreated (C), or TSA-treated cells (TSA) are shown together with samples exposed to UV radiation (UV), or exposed after TSA treatment (TSA+UV). (B) Normalised fluorescence intensity of BrdU immunofluorescence in G1-phase cells, measured by flow cytometry. Mean values ± s.d. (n=3) are reported. *P<0.05 compared with levels in the UV sample (Student's t-test). (C) HeLa cells expressing pEGFP, or p21-GFP, were UV-C irradiated (20 J/m²), incubated for 2 hours in [³H]thymidine and then fixed. Cells were immunostained with anti-GFP primary antibody and HRP-conjugated secondary antibody, and detected by immunoperoxidase staining (brown precipitate). UDS is denoted by the presence of nuclear autoradiographic granules. (D) Quantification of UDS grains in non-S-phase nuclei. Mean values of grain number (± s.d.) in duplicate samples, are reported. Bars, 10 µm (A,C).