Phosphorylation of p53 is required for the UV-induced XPA nuclear import.

<p><b>A.</b> Mitotically synchronized A549 cells were mock-treated or irradiated with 20 J/m² of UV-C, and allowed a 2-hr recovery before accessing the phosphorylation of p53 at Ser15 by Western blotting. <b>B.</b> Constructs for expressing human wild-type p53 or the S15A mutant of p53 were co-transfected with p53 3′-UTR siRNA into A549 cells. 72 hours after transfection, the A549 cells were mock- or UV (20 J/m²)-treated and allowed a 2-hr recovery. The UV-induced phosphorylation of p53 and the XPA in the nuclear fraction then were analyzed by Western blotting. The right panel shows the efficiency of siRNA knockdown of endogenous p53 and the level of recombinant p53 in the cells co-transfected with p53 3′-UTR siRNA and p53-WT constructs.