H4-Lys-16 (H4K16Ac) acetylation promotes H3 tail acetylation
turnover in a bromodomain-dependent manner. A, a comparison of
HAT activity of wild-type SAGA complex on nucleosome arrays containing
H4-Lys-16 acetylation (solid circles) and wild-type nucleosome arrays
(open circles). From the fitting of the data, for H4-Lys-16
acetylated nucleosomal arrays (solid line), the half-saturation
concentration is 19.7 ± 1.7 nm, and the kcat,
app is 2.64 ± 0.29 min-1. For the arrays that were not
preacetylated (dashed lines), the half-saturation concentration is
33.6 ± 5.0 nm with a kcat, app of 1.42
± 0.15 min-1. B, a comparison of HAT activity of
the SAGA Gcn5-Y413A complex on nucleosome arrays containing H4-Lys-16
acetylation (solid circles) and wild-type nucleosome arrays (open
circles). Two independent experiments were performed for H4-Lys-16
acetylated nucleosomes at each nucleosome concentration. Fitting of the data
give a half-saturation concentration and kcat, app of 98.1
nm and 1.50 min-1 for the H4-Lys-16 acetylated
nucleosome arrays (solid line) and 104.7 ± 29.7 nm
and 1.46 ± 0.15 min-1 for the wild-type nucleosome arrays
(dashed line). C, a comparison of the histone specificity of
the SAGA complex for wild-type (lane 2) and H4-Lys-16 acetylated
(lane 4) nucleosome arrays. Histones are resolved by SDS-PAGE.
Staining with Coomassie Blue is shown in the upper panel, with the
corresponding fluorogram shown in the lower panel. D, a comparison of
the sites of SAGA-mediated acetylation for nucleosomal arrays that are not
preacetylated (white column) and for nucleosome arrays that are
preacetylated at H4-Lys-16 (black column). The amount of
[3H]acetyl incorporation at a given position of the H3 tail was
determined by microsequencing. To more clearly compare the relative site
selectivity between nucleosome substrates, the data for the H4-Lys-16
preacetylated substrate have been normalized so that its total H3 histone
acetylation is equivalent to the total H3 acetylation for substrate that was
not preacetylated.