Figure 3. Hbo1 is the sole acetyltransferase in the Hbo1 protein complex.

A549 cells were infected with adenoviral vectors expressing either wild type (“Hbo1”) or catalytically dead (“Hbo1-G485A”) Hbo1 and immunoprecipitates were prepared using anti-Hbo1 antibody. The immunoprecipitates were assayed for HAT activity in reactions containing [³H]-acetylCoA and chicken core histones. (A) HAT activity. The incorporation of [³H]-acetate is plotted in the top panel. HAT reactions were spotted on P81 filters, washed, and assayed by scintillation counting. The recovery of Hbo1 in the immunoprecipitates, as assayed by western blot, is shown in the bottom panel. The left lane (“beads”) represents a mock immunoprecipitate prepared without primary antisera from cells infected with the wild type Hbo1 adenovirus. (B) Substrate specificity. HAT reactions were separated by electrophoresis on a 15% SDS-PAGE gel. The top panel shows the histone content of the reactions by Coomassie staining. The bottom panel shows the [³]-labeled histones visualized by fluorography.