A histone acetyltransferase (HAT) can be defined as an enzyme that acetylates core histones, which results in important regulatory effects on chromatin structure and assembly, and gene transcription. HATs are evolutionarily conserved from yeast to humans, that HATs generally contain multiple subunits, and that the functions of the catalytic subunit depend largely on the context of the other subunits in those complexes.  Histone acetylation is a dynamic reversible process. The balance of histone acetylation is important for proper cellular function and the cell has evolved enzymes that catalyse the removal of acetyl groups, termed histone deacetylases (HDACs). Histone acetyltransferases are a diverse set of enzymes that can be grouped on the basis of their catalytic domains. Some subunits have domains that cooperate to recruit the HAT to the appropriate location in the genome; these include bromodomains, chromodomains, WD40 repeats, Tudor domains and PHD fingers.


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