FIG. 1.

hRpb1 levels following UV irradiation and 4-NQO treatment of HeLa cells. HeLa cells were irradiated with 254-nm UV light at 22.5 J per m² as described in Materials and Methods, and cell extracts were prepared immediately or 1 or 4 h postirradiation. For 4-NQO treatment, the chemical was added directly to the culture medium at a final concentration of 0.5 μg/ml, and cell extracts were prepared immediately or 1 or 4 h later. Relative hRpb1 levels were determined by SDS-PAGE and immunoblotting and quantitated by densitometry. Levels are expressed as the percentage of Rpb1 remaining relative to the level in untreated cells.