When one of the two H3 tails in a nucleosome is acetylated, the Gcn5
bromodomain promotes acetylation of the other H3 tail. A, a
comparison of wild-type SAGA HAT activity on mononucleosomes containing
Tetra-Ac H3/WT H3 (solid circles) or Tetra-Ala H3/WT H3 (open
circles) octamers. Fitting of the data gives a half-saturation
concentration of 11.5 ± 2.4 nm (Tetra-Ac H3/WT H3
nucleosomes, solid line) and 38.9 ± 6.9 nm
(Tetra-Ala H3/WT H3 nucleosomes, dashed line). Data were adapted from
Li and Shogren-Knaak (17)
B, a comparison of HAT activity of SAGA Gcn5-Y413A complex on
mononucleosomes containing Tetra-Ac H3/WT H3 (open circles) and
Tetra-Ala H3/WT H3 (solid circles) octamers. Two independent
experiments were performed at each nucleosome concentration. The
half-saturation concentrations obtained from fitting the data are 30.6
nm (Tetra-Ac H3/WT H3 nucleosomes, dashed line) and 32.8
nm (Tetra-Ala H3/WT H3 nucleosomes, solid line).
C, a fluorogram showing the histone specificity of SAGA acetylation
on mononucleosomes that are either preacetylated or unacetylated on one H3
histone tail (lanes 1 and 2, respectively). The Coomassie
Blue-stained gel (upper panel) and corresponding fluorogram
(lower panel) are shown.