ABSTRACT

Histone modification map of H4 N-terminal tail residues in Saccharomyces cerevisiae reveals the prominence of lysine acetylation. Previous reports have indicated the importance of lysine acetylation in maintaining chromatin structure and function. H4K16, a residue with highly regulated acetylation dynamics has unique functions not overlapping with the other H4 N- terminal acetylable residues. The present work unravels the role of H4K16 acetylation in regulating expression of constitutive genes. H4K16 gets distinctly deacetylated over the coding region of constitutively expressed genes. Deacetylation of H4K16 reduces H3K9 acetylation at the cellular and gene level. Reduced H3K9 acetylation however did not negatively correlate with active gene transcription. Significantly, H4K16 deacetylation was found to be associated with hypoacetylated H4K12 throughout the locus of constitutive genes. H4K16 and K12 deacetylation is known to favour active transcription. Sas2, the HAT mutant showed similar patterns of hypoacetylated H3K9 and H4K12 at the active loci, clearly implying that the modifications were associated with deacetylation state of H4K16. Deacetylation of H4K16 was also concurrent with increased H3K56 acetylation in the promoter region and ORF of the constitutive genes. Combination of all these histone modifications significantly reduced H3 occupancy, increased promoter accessibility and enhanced RNAPII recruitment at the constitutively active loci. Consequently, we found that expression of active genes was higher in H4K16R mutant which mimic deacetylated state, but not in H4K16Q mimicking constitutive acetylation. To summarize, H4K16 deacetylation linked with H4K12 and H3K9 hypoacetylation along with H3K56 hyperacetylation generate a chromatin landscape that is conducive for transcription of constitutive genes.

摘要

酿酒酵母H4 N 末端尾残基的组蛋白修饰图揭示了赖氨酸乙酰化的显着性。以前的报道表明赖氨酸乙酰化在维持染色质结构和功能方面的重要性。H4K16 是一种具有高度调节的乙酰化动力学的残基，具有独特的功能，不会与其他 H4 N 端可乙酰化残基重叠。目前的工作揭示了 H4K16 乙酰化在调节组成基因表达中的作用。H4K16 在组成型表达基因的编码区明显脱乙酰化。H4K16 的去乙酰化降低了细胞和基因水平的 H3K9 乙酰化。然而，减少的 H3K9 乙酰化与活性基因转录没有负相关。值得注意的是，发现 H4K16 去乙酰化与整个组成基因位点的低乙酰化 H4K12 相关。SAS2，HAT 突变体在活性位点显示出相似的低乙酰化 H3K9 和 H4K12 模式，这清楚地表明这些修饰与 H4K16 的去乙酰化状态有关。H4K16 的去乙酰化也与组成基因的启动子区域和 ORF 中增加的 H3K56 乙酰化同时发生。所有这些组蛋白修饰的组合显着降低了 H3 的占有率，增加了启动子的可及性并增强了组成型活性位点的 RNAPII 募集。因此，我们发现在模拟去乙酰化状态的 H4K16R 突变体中活性基因的表达更高，但在模拟组成型乙酰化的 H4K16Q 中则不然。总结一下，