Histone H4 acetylation of euchromatin and heterochromatin is cell cycle dependent and correlated with replication rather than with transcription

Reversible acetylation of nucleosomal histones H3 and H4 generally is belie ved 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 rat her than with transcriptional activity, whereas H3 acetylation remains fair ly constant throughout the cell cycle. Compared with euchromatin, plant nuc leolus organizers were more strongly acetylated at H4 during mitosis but le ss acetylated during S phase, when the nucleolus appeared to be (at least t ransiently) devoid of nucleosomes. Deposition-related acetylation of lysine s 5 and 12 of H4 seems to be conserved in animals and plants and extended t o K16 in plants. A possibly species-specific above-average acetylation at l ysines 9/18 and 14 of H3 appeared in 4',6-diamidino-2-phenylindole (DAPI)-s tained heterochromatin fractions. These results were obtained by combining immunodetection of all acetylatable isoforms of H3 and H4 on mitotic chromo somes 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 s itu hybridization or DAPI staining. In addition, the histone acetylation pa tterns of distinct domains were compared with their replication and transcr iption patterns.