Targeted and extended acetylation of histones H4 and H3 at active and inactive genes in chicken embryo erythrocytes

Affinity-purified polyclonal antibodies recognizing the most highly acetylated forms of histones H3 and H4 were used in immunoprecipitation assays with chromatin fragments derived from 15-day chicken embryo erythrocytes by micrococcal nuclease digestion. The distribution of hyperacetylated H4 and H3 was mapped at the housekeeping gene, glyceraldehyde S-phosphate dehydrogenase (GAPDH), and the tissue-specific gene, carbonic anhydrase (CA), H3 and H4 acetylation was found targeted to the CpG island region at the 5' end of both these genes, falling off in the downstream direction. In contrast, at the beta (A)-globin gene, both H3 and H4 are highly acetylated throughout the gene and at the downstream enhancer, with a maximum at the promoter. Low level acetylation was observed at the 5' end of the inactive ovalbumin gene. Run-on assays to measure ongoing transcription showed that the GAPDH and CA genes are transcribed at a much lower rate than the adult beta (A)-globin gene. The extensive high level acetylation at the beta (A)-globin gene correlates most simply with its high rate of transcription. The targeted acetylation of histones H3 and H4 at the GAPDH and CA genes is consistent with a role in transcriptional initiation and implies that transcriptional elongation does not necessarily require hyperacetylation.