Histone H4 Acetylation of Euchromatin and Heterochromatin Is Cell Cycle Dependent and Correlated with Replication Rather Than with Transcription

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Abstract
Reversible acetylation of nucleosomal histones H3 and H4 generally is believed to be correlated with potential transcriptional activity of eukaryotic chromatin domains. Here, we report that the extent of H4 acetylation within euchromatin and heterochromatic domains is linked with DNA replication rather than with transcriptional activity, whereas H3 acetylation remains fairly constant throughout the cell cycle. Compared with euchromatin, plant nucleolus organizers were more strongly acetylated at H4 during mitosis but less acetylated during S phase, when the nucleolus appeared to be (at least transiently) devoid of nucleosomes. Deposition-related acetylation of lysines 5 and 12 of H4 seems to be conserved in animals and plants and extended to K16 in plants. A possibly species-specific above-average acetylation at lysines 9/18 and 14 of H3 appeared in 4',6-diamidino-2-phenylindole (DAPI)-stained heterochromatin fractions. These results were obtained by combining immunodetection of all acetylatable isoforms of H3 and H4 on mitotic chromosomes and nuclei in G1, early S, mid-S, late S, and G2 phases of the field bean with identification of specific chromatin domains by fluorescence in situ hybridization or DAPI staining. In addition, the histone acetylation patterns of distinct domains were compared with their replication and transcription patterns.