Histone acetylation: plants and fungi as model systems for the investigation of histone deacetylases.

The basic element of chromatin is the nucleosome. Histones H4, H3, H2A and H2B form the core histone octamer by protein-protein interactions of their folded domains. The free, flexible N-terminal extensions of the histones protrude from the nuclesome; they contain conserved lysines undergoing posttranslational acetylation. Histone acetyltransferases (HATs) transfer the acetyl moiety of acetyl-coenzyme A to the epsilon-amino group; this reaction is reverted by histone deacetylases (HDACs). The dynamic equilibrium of the acetylation/deacetylation reaction varies throughout the genome; some regions in chromatin undergo rapid acetylation/deacetylation, whereas others are fixed in a certain acetylation state without significant changes. In general, chromatin regions engaged in transcription display dynamic acetylation, i.e. HATs and HDACs are recruited to these regions. Higher plants and fungi have considerably contributed to the unraveling of the multiplicity of HDACs; in particular, plants possess HDACs that have so far not been identified in animal cells.