HATs are traditionally divided into two different classes based on their subcellular localization.
Type A HATs are located in the nucleus and are involved in the regulation of gene expression through acetylation of nucleosomal histones in the context of chromatin.
 They contain a bromodomain, which helps them recognize and bind to acetylated lysine residues on histone substrates.
Gcn5, p300/CBP, and TAFII250 are some examples of type A HATs that cooperate with activators to enhance transcription.
Type B HATs are located in the cytoplasm and are responsible for acetylating newly synthesized histones prior to their assembly into nucleosomes.
These HATs lack a bromodomain, as their targets are unacetylated.
The acetyl groups added by type B HATs to the histones are removed by HDACs once they enter the nucleus and are incorporated into chromatin.
Hat1 is one of the few known examples of a type B HAT.
 Despite this historical classification of HATs, some HAT proteins function in multiple complexes or locations and would thus not easily fit into a particular class.
HATs are traditionally divided into two different classes based on their subcellular localization. Type A HATs are located in the nucleus and are involved in the regulation of gene expression through acetylation of nucleosomal histones in the context of chromatin.  They contain a bromodomain, which helps them recognize and bind to acetylated lysine residues on histone substrates. Gcn5, p300/CBP, and TAFII250 are some examples of type A HATs that cooperate with activators to enhance transcription. Type B HATs are located in the cytoplasm and are responsible for acetylating newly synthesized histones prior to their assembly into nucleosomes. These HATs lack a bromodomain, as their targets are unacetylated. The acetyl groups added by type B HATs to the histones are removed by HDACs once they enter the nucleus and are incorporated into chromatin. Hat1 is one of the few known examples of a type B HAT.  Despite this historical classification of HATs, some HAT proteins function in multiple complexes or locations and would thus not easily fit into a particular class.
Histone acetyltransferase