C646 treatment reduces histone H3 and H4 acetylation levels and abrogates TSA-induced acetylation in cells. Quiescent C3H 10T1/2 mouse fibroblasts were pretreated with C646 (25 uM, lanes 2-4, 6-8) for the indicated times (1, 2 or 3h) or the control compound, C37 (25 uM, 3h, lanes 9, 10), and TSA (33 nM) added where indicated (lanes 6-8, 10) for the final 30 min of incubation. Histones were extracted and analysed by western blotting to visualize total H3 and H3K9ac using SDS (Panel A) or H3, H3K9ac, and H4K12ac using acid-urea (Panel B) gel electrophoresis. Acid-urea gels separate histones on the basis of charge. Each acetylation event incrementally retards migration to produce a ‘ladder’ of bands, numbers on either side of the blot indicating extent of modification. (lane 1, untreated control cells; lane 5, TSA-treated cells).