Snf1p-dependent Spt-Ada-Gcn5-acetyltransferase (SAGA) recruitment and chromatin remodeling activities on the HXT2 and HXT4 promoters

We previously showed that the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex is recruited to the activated HXT2 and HXT4 genes and plays a role in the association of TBP-associated factors. Using the HXT2 and HXT4 genes, we now present evidence for a functional link between Snf1p-dependent activation, recruitment of the SAGA complex, histone H3 removal, and H3 acetylation. Recruitment of the SAGA complex is dependent on the release of Ssn6p-Tup1p repression by Snf1p. In addition, we found that the Gcn5p subunit of the SAGA complex preferentially acetylates histone H3K18 on the HXT2 and HXT4 promoters and that Gcn5p activity is required for removal of histone H3 from the HXT4 promoter TATA region. In contrast, histone H3 removal from the HXT2 promoter does not require Gcn5p. In conclusion, although similar protein complexes are involved, induction of HXT2 and HXT4 displays important mechanistic differences.     

Histone acetyltransferase general control non‐repressed protein 5 (GCN5) affects the fatty acid composition of Arabidopsis thaliana seeds by acetylating fatty acid desaturase3 (FAD3)

Seed oils are important natural resources used in the processing and preparation of food. Histone modifications represent key epigenetic mechanisms that regulate gene expression, plant growth and development. However, histone modification events during fatty acid (FA) biosynthesis are not well understood. Here, we demonstrate that a mutation of the histone acetyltransferase GCN5 can decrease the ratio of α‐linolenic acid (ALA) to linoleic acid (LA) in seed oil. Using RNA‐Seq and ChIP assays, we identified FAD3, LACS2, LPP3 and PLAIIIβ as the targets of GCN5. Notably, the GCN5‐dependent H3K9/14 acetylation of FAD3 determined the expression levels of FAD3 in Arabidopsis thaliana seeds, and the ratio of ALA/LA in the gcn5 mutant was rescued to the wild‐type levels through the overexpression of FAD3. The results of this study indicated that GCN5 modulated FA biosynthesis by affecting the acetylation levels of FAD3. We provide evidence that histone acetylation is involved in FA biosynthesis in Arabidopsis seeds and might contribute to the optimization of the nutritional structure of edible oils through epigenetic engineering.     

A glycolytic burst drives glucose induction of global histone acetylation by picNuA4 and SAGA

Little is known about what enzyme complexes or mechanisms control global lysine acetylation in the amino-terminal tails of the histones. Here, we show that glucose induces overall acetylation of H3 K9, 18, 27 and H4 K5, 8, 12 in quiescent yeast cells mainly by stimulating two KATs, Gcn5 and Esa1. Genetic and pharmacological perturbation of carbon metabolism, combined with ¹H-NMR metabolic profiling, revealed that glucose induction of KAT activity directly depends on increased glucose catabolism. Glucose-inducible Esa1 and Gcn5 activities predominantly reside in the picNuA4 and SAGA complexes, respectively, and act on chromatin by an untargeted mechanism. We conclude that direct metabolic regulation of globally acting KATs can be a potent driving force for reconfiguration of overall histone acetylation in response to a physiological cue.     

The yeast histone acetyltransferase A2 complex, but not free Gcn5p, binds stably to nucleosomal arrays

We have investigated the structural basis for the differential catalytic function of the yeast Gcn5p-containing histone acetyltransferase (HAT) A2 complex and free recombinant yeast Gcn5p (rGcn5p). HAT A2 is shown to be a unique complex that contains Gcn5p, Ada2p, and Ada3p, but not proteins specific to other related HAT A complexes, e.g. ADA, SAGA. Nevertheless, HAT A2 produces the same unique polyacetylation pattern of nucleosomal substrates reported previously for ADA and SAGA, demonstrating that proteins specific to the ADA and SAGA complexes do not influence the enzymatic activity of Gcn5p within the HAT A2 complex. To investigate the role of substrate interactions in the differential behavior of free and complexed Gcn5p, sucrose density gradient centrifugation was used to characterize the binding of HAT A2 and free rGcn5p to intact and trypsinized nucleosomal arrays, H3/H4 tetramer arrays, and nucleosome core particles. We find that HAT A2 forms stable complexes with all nucleosomal substrates tested. In distinct contrast, rGcn5p does not interact stably with nucleosomal arrays, despite being able to specifically monoacetylate the H3 N terminus of nucleosomal substrates. Our data suggest that the ability of the HAT A2 complex to bind stably to nucleosomal arrays is functionally related to both local and global acetylation by the complexed and free forms of Gcn5p.