Figure 5. Depletion of HBO1 or mutant HBO1 causes defective CPD repair and increases sensitivity to ultraviolet irradiation.

(a,b) ShCtl, shDDB2 and shHBO1 (a) or shHBO1 Myc-HBO1 WT, EQ or SA-expressing cells (b) were not irradiated (-ultraviolet) or irradiated with 12 J m⁻² ultraviolet, and then cultured for 0, 1, 8 and 24 h. Cells were then fixed and immunostained with anti-CPD antibody and DNA was counterstained with DAPI. Relative intensities of CPD normalized against DAPI are shown as fold of ultraviolet 0 h cells. Cells (n=50) from three independent experiments; error bars indicate means±s.d. **P<0.01 (Student’s t-test). (c,d) ShCtl, shDDB2 and shHBO1 (c) or shHBO1 and shHBO1 Myc-HBO1 WT, EQ or SA-expressing cells (d) were irradiated at the indicated ultraviolet dose. Cells were cultured for 2 weeks and then fixed with MeOH/acetic acid and stained with crystal violet solution. The numbers of colonies were counted and are represented as % of mock-irradiated cells. Three independent experiments were performed. Error bars indicate means±s.d.