Jasencakova Z, Meister A, Schubert I
Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Gatersleben, Germany.
Chromosoma. 2001 May;110(2):83-92. doi: 10.1007/s004120100132.
We have studied the replication time, nuclear organization and histone acetylation patterns of distinct chromatin domains [nucleolus organizers (NORs), centromeres, euchromatin and heterochromatin] of barley during the cell cycle. The Rabl orientation of chromosomes, with centromeres and telomeres located at opposite nuclear poles, was found to be maintained throughout interphase. Replication started at the rDNA loci within nucleoli and then proceeded from the euchromatic distal chromosome regions toward the heterochromatic pole. Centromere association frequently occurred in mid- and late S-phase, i.e., during and after centromere replication. Euchromatin, centromeres and heterochromatin were found to be enriched in acetylated histone H4 (except for lysine 16) during their replication; then deacetylation occurred. The level of deacetylation of H4 in heterochromatin was more pronounced than in euchromatin. Deacetylation is finished in early G2-phase (lysine 8) or may last until mitosis or even the next G1-phase (lysines 5 and 12). The NORs were found to be most strongly acetylated at lysines 5 and 12 of H4 during mitosis, independently of their potential activity in nucleolus formation and rDNA transcription. The acetylation pattern of chromosomal histone H3 was characterized by low acetylation intensity at centromeres (lysines 9/18) and pericentromeric regions (lysine 14) and more intense uniform acetylation of the remaining chromatin; it remained fairly constant throughout the cell cycle. These results have been compared with the corresponding data published for mammals and for the dicot Vicia faba. This revealed conserved features as well as plant- or species-specific peculiarities. In particular, the connection of acetylation intensity of H4 at microscopically identifiable chromatin domains with replicational but not with transcriptional activity during the cell cycle seems to be conserved among eukaryotes.
我们研究了大麦在细胞周期中不同染色质结构域[核仁组织区（NORs）、着丝粒、常染色质和异染色质]的复制时间、核组织及组蛋白乙酰化模式。发现染色体的拉布尔定向（着丝粒和端粒位于相对的核极）在整个间期都得以维持。复制始于核仁内的rDNA位点，然后从常染色质远端染色体区域向异染色质极进行。着丝粒关联经常发生在S期中期和后期，即着丝粒复制期间及之后。常染色质、着丝粒和异染色质在复制期间被发现富含乙酰化组蛋白H4（赖氨酸16除外）；然后发生去乙酰化。异染色质中H4的去乙酰化水平比常染色质中更明显。H4的去乙酰化在G2期早期（赖氨酸8）完成，或者可能持续到有丝分裂甚至下一个G1期（赖氨酸５和12）。发现NORs在有丝分裂期间H4的赖氨酸5和12处乙酰化程度最强，与它们在核仁形成和rDNA转录中的潜在活性无关。染色体组蛋白H3的乙酰化模式特征为着丝粒（赖氨酸9/18）和着丝粒周围区域（赖氨酸14）的乙酰化强度低，其余染色质的乙酰化均匀且强度更高；在整个细胞周期中保持相当稳定。已将这些结果与针对哺乳动物和双子叶植物蚕豆发表的相应数据进行了比较。这揭示了保守特征以及植物或物种特异性的特性。特别是，在细胞周期中，微观可识别染色质结构域处H4的乙酰化强度与复制活性而非转录活性之间的联系在真核生物中似乎是保守的。
