text: Histone acetyltransferase (HATs) Histone Acetyltransferases, also known as HATs, are a family of enzymes that acetylate the histone tails of the nucleosome. This, and other modifications, are expressed based on the varying states of the cellular environment. Many proteins with acetylating abilities have been documented and, after a time, were categorized based on sequence similarities between them. These similarities are high among members of a family, but members from different families show very little resemblance. Some of the major families identified so far are as follows.
  GNAT family
  General Control Non-Derepressible 5 (Gcn5) –related N-Acetyltransferases (GNATs) is one of the many studied families with acetylation abilities. This superfamily includes the factors Gcn5 which is included in the SAGA, SLIK, STAGA, ADA, and A2 complexes, Gcn5L, p300/CREB-binding protein associated factor (PCAF), Elp3, HPA2 and HAT1. Major features of the GNAT family include HAT domains approximately 160 residues in length and a conserved bromodomain that has been found to be an acetyl-lysine targeting motif. Gcn5 has been shown to acetylate substrates when it is part of a complex. Recombinant Gcn5 has been found to be involved in the acetylation of the H3 histones of the nucleosome.  To a lesser extent, it has been found to also acetylate H2B and H4 histones when involved with other complexes.  PCAF has the ability to act as a HAT protein and acetylate histones, it can acetylate non-histone proteins related to transcription, as well as act as a coactivator in many processes including myogenesis, nuclear-receptor-mediated activation and growth-factor-signaled activation. Elp3 has the ability to acetylate all histone subunits and also shows involvement in the RNA polymerase II holoenzyme.