Figure 2. Cell cycle checkpoint proteins Chk1 and MK2 are not required in the UV-induced nuclear import of XPA.

A. siRNA duplexes targeting Chk1 were transiently transfected into A549 cells, followed by mock or 20 J/m² UV irradiation and a 2-hr recovery. The localization of XPA was assessed using subcellular fractionation followed by Western blot analysis. PARP and β-actin proteins were probed as nuclear and cytoplasmic protein controls, respectively. B. A549 cells were treated with MK2 or control siRNA, followed by UV irradiation. After a 2-hr recovery period, irradiated cells were fractioned and analyzed by Western blotting. C. Chk1 and MK2 were simultaneously knocked down by Chk1 and MK2 siRNAs, or ATR was knocked down by ATR siRNA. Then, the UV-induced XPA nuclear import in these cells was assessed by fractionation and Western blotting.