Histone acetyltransferase complexes: one size doesn't fit all

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Abstract
Histone acetyltransferase (HAT) enzymes are a diverse group of proteins that are evolutionarily conserved from yeast to humans. Although originally identified as enzymes that acetylate histones, a growing number of non-histone substrates have been identified for HATs, which implies a more general role in regulating the function of an ever-growing number of proteins. Based on structural evidence, HAT enzymes can accommodate a number of substrates; therefore, the functions of these enzymes are much more varied than simply modifying histones post-translationally. Although the HAT enzyme is the catalytic subunit that is required for activity, it is the context in which these enzymes exist that provides the enzyme with specificity. Most HAT enzymes exist in multiprotein complexes, and it is these proteins that allow the enzymes to carry out specific functions in the cell. Many HAT-associated proteins contain domains, which can recognize and bind modified protein residues. This includes bromo-, chromo- and PHD (plant homeodomain) domains, which are able to bind modified histones. HAT enzymes carry out several functions in the cell, ranging from repairing regions of DNA damage to maintaining overall genomic integrity. Future work needs to focus on understanding developmental and tissue-specific HAT complexes while continuing to explore the mechanisms by which an organism maintains the balance of acetylation.