from Anne K. Voss and Tim Thomas writing in Epigenetics: A Reference Manual:
A histone (H3-H4)2 tetramer flanked by two H2A-H2B heterodimers form the core protein structure, around which DNA is wrapped. DNA and the histone octamer together form the smallest chromatin particle, the nucleosome. How intimately the DNA associates with the core histones and how tightly the nucleosomes are packed with each other is determined by a key post-translational modification of the histone proteins, namely acetylation. Histone acetylation was first discovered in the early 1960s. After a dearth of progress, due to technical limitations, our knowledge of histone acetylation has exploded in the last fifteen years. Enzymes that catalyse acetylation of histones, the histone acetyltransferases, have been discovered, proteins associated with these have been identified and their preferences for specific histone residues have been determined. Importantly, we are gaining a better understanding of the relevance of histone acetylation in health and disease through the discovery of genetic mutations underlying human diseases in loci encoding histone acetyltransferases (HATs) and through examination of mouse strains deficient in specific histone acetyltransferases. Here we discuss the principles of histone acetyltransferase biology.
Further reading: Epigenetics: A Reference Manual