Figure 4. HBO1 acetylates histone H3 and H4 around DDB2-bound chromatin after ultraviolet irradiation.

(a) Acetylation levels of histone H3 Lys 14 and histone H4 around HA-DDB2-bound chromatin were increased after ultraviolet irradiation. Transiently expressing HA-DDB2 cells were irradiated with 40 J m⁻² ultraviolet and collected at 0, 20 and 120 min. Cells were cross-linked and immunoprecipitated as described in Methods. Immunoprecipitates were then subjected to western blotting with the indicated antibodies. Signal intensities were quantitated using ImageJ. Error bars indicate means±s.d. from seven independent experiments. *P<0.05; **P<0.01 (Student’s t-test). (b) Acetylation levels of histones around HA-DDB2-bound chromatin after ultraviolet irradiation were HBO1-dependently increased. HA-DDB2-expressing shCtl and shHBO1 cells were mock irradiated or irradiated with 40 J m⁻² ultraviolet and collected after 20 min ultraviolet irradiation. ChIP-western blotting was performed as described in a. Signal intensities were quantitated using ImageJ. Error bars indicate means±s.d. from five independent experiments. *P<0.05, **P<0.01 (Student’s t-test).