Nucleosomal acetylation

One obtains 63% of pBR control nucleosomes in the closed negative state against 28% in the open state, with approximately reverse figures for the same acetylated nucleosomes in phosphate respectively 32% against 65% (complements to 100% are closed positive nucleosomes). 

The structure of the acetylated nucleosome core particle The early characterization of acetylated nucleosomes suggested that this histone modification imparted some important structural changes at the level of the nucleosome core particle. It was found that the flanking DNA regions at the entry... 

Hassan, A.H., Awad, S. and Prochasson, P. (2006) The Swi2/Snf2 bromodomain is required for the displacement of SAGA and the octamer transfer of SAGA-acetylated nucleosomes. The Journal of Biological Chemistry, 281, 18126-18134. 

Chromatin is composed of nucleosomes, where each comprise 147 base pairs of DNA wrapped around an octamer oftwo copies of each histone H2A, H2B, H3, and H4. Nucleosomes are folded into higher-order structures that are stabilized by linker histones. Chromatin structure can be altered by enzymes that posttranslationally modify histones (e.g., through phosphorylation, acetylation, methylation, or ubiquitination) or by ATP-driven chromatin-remodeling complexes that alter nucleosome position and/or composition. 

An enzyme activity ascribed to many coactivators, which transfers acetyl groups to lysine residues of histone tails of the nucleosomes and thereby facilitate their disruption and the opening of the chromatin. 

Enzyme activity ascribed to corepressors, which is the removal of acetyl groups from lysine residues of histone tails. Thereby the assembly of nucleosomes is maintained, which leads to a dense, transcriptional inactive chromatin structure. 

Histone tails are the N-terminal regions of histones which reach outside the nucleosomes. They are not essential for the formation in of nucleosomes but are required for the formation of higher-order chromatin structures. The histone tails are also known to be heavily posttranslationally modified by acetylation, phosphorylation, methylation, etc. and are important for the regulation of gene activity. 

The core unit of the chromatin, the nucleosome, consists of histones arranged as an octamer consisting of a (H3/ H4)2-tetramer complexed with two histone H2A/H2B dimers. Accessibility to DNA-binding proteins (for replication, repair, or transcription) is achieved by posttranslational modifications of the amino-termini of the histones, the histone tails phosphorylation, acetylation, methylation, ubiquitination, and sumoyla-tion. Especially acetylation of histone tails has been linked to transcriptional activation, leading to weakened interaction of the core complexes with DNA and subsequently to decondensation of chromatin. In contrast, deacetylation leads to transcriptional repression. As mentioned above, transcriptional coactivators either possess HAT activity or recruit HATs. HDACs in turn act as corepressors. 

Fig. 10.2. FSPIM analysis of the interaction between maize transcriptional coactivators—GCN5 and ADA2—fused to CFP and YFP. GCN5 is a histone acetyltransferase that, in conjunction with adaptor protein ADA2, modulates transcription in diverse eukaryotes by affecting the acetylation status of the core histones in nucleosomes [63]. CFP- and YFP-tagged proteins, expressed in protoplasts, were excited by the 458 nm and the 514 nm laser lines sequentially. CFP fluorescence was selectively detected by an FIFT 458 dichroic mirror and BP 470-500 band pass emission filter while YFP fluorescence was selectively detected by using an HFT 514 dichroic mirror and...

The histones, which provide the nucleosomes with their structural base, are susceptible to acetylation. Receptors bound to antagonists, or even... 

One of the most-studied covalent modifications is the acetylation of the lysine residues of histone tails. The acetylation state of lysines of nucleosomal histones modulates chromatin structure and regulates gene transcriptional activity. The balance of lysine acetylation is controlled by the antagonistic action of two enzyme families histone deacetylases (HDACs) and histone acetyltransferases (HATs). In humans there are essentially three main HDAC subclasses [6]. 

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