Transitions in histone acetylation reveal boundaries of three separately regulated neighboring loci

We have studied developmentally regulated patterns of histone acetylation a t high resolution across similar to 54 kb of DNA containing three independe ntly regulated but neighboring genetic loci. These include a folate recepto r gene, a 16 kb condensed chromatin region, the chicken beta -globin domain and an adjacent olfactory receptor gene. Within these regions the relative levels of acetylation appear to fall into three classes. The condensed chr omatin region maintains the lowest acetylation at every developmental stage . Genes that are inactive show similarly low levels, but activation results in a dramatic increase in acetylation. The highest levels of acetylation a re seen at regulatory sites upstream of the genes. These patterns imply the action of more than one class of acetylation. Notably, there is a very str ong constitutive focus of hyperacetylation at the 5' insulator element sepa rating the globin locus from the folate receptor region, which suggests tha t this insulator element may harbor a high concentration of histone acetyla ses.