"Wild-type and Nedd4 knockdown cells were subjected to UV irradiation, and Rpb1 levels were checked by immunoblotting. Significantly, the level of Rpb1 consistently decreased less dramatically in the knockdown cells (Figures 5E and 5F, compare lanes 6–10, and data not shown), indicating that Nedd4 is indeed required for UV-induced Rpb1 degradation. Treatment of cells with proteasome inhibitor prevented degradation (Figures 5E and 5F, lanes 1–5)." PMID:17996703