Fig. 5. Chk1 contains a functional NLS. (A) A strain expressing the chk1-4A mutant integrated at the chk1 locus was treated with 40 µM CPT and processed for immunofluorescence. (B) UV survival was measured for the indicated strains after exposure to 50, 100, 150 and 200 J/m2 UV. UV survival experiments were conducted in triplicate. (C) Western blotting was performed on protein lysates from the indicated strains that were treated with or without 40 µM CPT for 2.5 hours. Chk1 mobility shift was monitored after SDS-PAGE using anti-HA antibody. (D) A strain expressing the chk1-4A + SV40 NLS was treated with 40 µM CPT and processed for immunofluorescence. (E) UV survival was measured for the indicated strains as in B. (F) Addition of the SV40-NLS to wild-type Chk1 enhances nuclear localization as detected by immunofluorescence. Bars, 10 µm.