Histone acetylation in chicken erythrocytes. Rates of acetylation and evidence that histones in both active and potentially active chromatin are rapidly modified.

Of the modifiable histone lysine sites, 2-4% participate in dynamic acetylation in chicken erythrocytes, suggesting the involvement of no more than 1-2% of the total genome. The rates and chromatin locality of this dynamic acetylation were studied in both chicken mature and immature red blood cells. In mature erythrocytes, two rates of acetylation of radiolabelled, monoacetylated H4 are observed, with half-lives of approximately 12 and approximately 300 min. In contrast, only one rate with a half-life (t1/2) of 12 min is observed in immature cells, and further experiments rule out the possibility of a slow rate of acetylation (with a t1/2 of approximately 300 min) for any form of H4 in this cell type. The simplest interpretation of these quantitative results, taken together with the behaviour of H3, H2B and H4 observed on the fluorograms used for rate analysis, is that a portion of the rapidly acetylated histone is converted to a more slowly acetylated form during erythrocyte maturation. The transcriptionally active adult beta-globin and H5 nucleohistone, which are presumably converted to potentially active chromatin during the maturation process, remain of the rapidly acetylated form in the mature cell.