Histone Acetyl Transferases
HATs or histone acetyltransferases, are enzymes that play a role in transcription activation, and are known to function in multi-subunit complexes of two main types; GNAT and MYST. They work by acetylating lysine amino acids on histone proteins. Histone tails are positvely charged and can interact with the negatively charged backbone of a near by nucleosome to bring them together and act as a 'glue'. Acetylation results in the postive charge being lost, (the enzyme transfers an acetyl group from acetyl-CoA), which reduces the interaction and therefore the compaction. This is important as it reduces the affinity between the histone and DNA, as it is negatively charged, which makes the DNA more accessible to other transcription factors. However, this does not produce enough acetylation to impact chromatin structure so in addition to this the conformation change also produces protein-protein interaction domains called bromodomains. These bromodomains promote transcription as Bdf1 binds acetylated H4, and therefore recruits TFIID a subunit (TAFII250) of which also binds to the acetylated H4.
In the 1960s a correlation between acetylation and transcription was discovered. The first HAT was shown to be homologous to GCN5 in yeast, which was a monumental discovery as GCN5 was already known to function as a transcriptional activator.
Grunstein, M. (1997). Histone acetylation in chromatin structure and transcription. [online] Nature. Available at: https://www.nature.com/articles/38664 [Accessed 23 Oct. 2018].
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