Earley Keith W, Shook Molly S, Brower-Toland Brent, Hicks Leslie, Pikaard Craig S
Biology Department, Washington University, 1 Brookings Drive, St Louis, MO 63130, USA.
Plant J. 2007 Nov;52(4):615-26. doi: 10.1111/j.1365-313X.2007.03264.x. Epub 2007 Sep 18.
In genetic hybrids displaying nucleolar dominance, acetylation of lysines 5, 8, 12 and 16 of histone H4 (H4K5, H4K8, H4K12, H4K16) and acetylation of histone H3 on lysines 9 and 14 (H3K9, H3K14) occurs at the promoters of active ribosomal RNA (rRNA) genes, whereas silenced rRNA genes are deacetylated. Likewise, histone hyperacetylation correlates with the active state of transgenes and of endogenous plant genes involved in physiological processes, including cold tolerance, light-responsiveness and flowering. To investigate histone hyperacetylation dynamics we used sodium butyrate, a histone deacetylase inhibitor known to switch silent rRNA genes on, in order to enrich the pool of acetylated histones. Mass spectrometric analyses revealed unique mono- (K16Ac), di- (K12Ac, K16Ac), tri- (K8Ac, K12Ac, K16Ac), and tetra-acetylated (K5Ac, K8Ac, K12Ac, K16Ac) histone H4 isoforms, suggesting that H4 hyperacetylation occurs in a processive fashion, beginning with lysine 16 and ending with lysine 5. Using a combination of molecular and mass spectrometric assays we then determined the specificities of seven of the nine functional co-activator type histone acetyltransferases (HATs) in Arabidopsis thaliana: specifically HATs of the CBP (HAC1, HAC5, HAC12), GNAT (HAG1, HAG2), and MYST families (HAM1, HAM2). Specific HATs acetylate histone H4K5 (HAM1, HAM2), H4K12 (HAG2), and H3K14 (HAG1), suggesting that acetylation of these lysines may have special regulatory significance. Other acetylation events, including histone H3K9 acetylation, are likely to result from the activities of the broad-specificity HAC1, HAC5, and HAC12 histone acetyltransferases.
在表现出核仁显性的遗传杂种中，组蛋白H4赖氨酸5、8、12和16（H4K5、H4K8、H4K12、H4K16）的乙酰化以及组蛋白H3赖氨酸9和14（H3K9、H3K14）的乙酰化发生在活跃核糖体RNA（rRNA）基因的启动子处，而沉默的rRNA基因则发生去乙酰化。同样，组蛋白高度乙酰化与转基因以及参与生理过程（包括耐寒性、光反应性和开花）的内源性植物基因的活跃状态相关。为了研究组蛋白高度乙酰化动力学，我们使用了丁酸钠，一种已知能开启沉默rRNA基因的组蛋白去乙酰化酶抑制剂，以富集乙酰化组蛋白池。质谱分析揭示了独特的单乙酰化（K16Ac）、二乙酰化（K12Ac、K16Ac）、三乙酰化（K8Ac、K12Ac、K16Ac）和四乙酰化（K5Ac、K8Ac、K12Ac、K16Ac）的组蛋白H4异构体，这表明H4高度乙酰化以一种渐进的方式发生，从赖氨酸16开始，到赖氨酸5结束。然后，我们结合分子和质谱分析方法，确定了拟南芥中九种功能性共激活剂型组蛋白乙酰转移酶（HATs）中的七种的特异性：具体为CBP家族（HAC1、HAC5、HAC12）、GNAT家族（HAG1、HAG2）和MYST家族（HAM1、HAM2）的HATs。特定的HATs使组蛋白H4K5（HAM1、HAM2）、H4K12（HAG2）和H3K14（HAG1）乙酰化，这表明这些赖氨酸的乙酰化可能具有特殊的调节意义。其他乙酰化事件，包括组蛋白H3K9乙酰化，可能是由具有广泛特异性的HAC1、HAC5和HAC12组蛋白乙酰转移酶的活性导致的。
