Ma X J, Wu J, Altheim B A, Schultz M C, Grunstein M
Department of Biological Chemistry, University of California Los Angeles School of Medicine, and the Molecular Biology Institute, University of California, Los Angeles, CA 90095, USA.
Proc Natl Acad Sci U S A. 1998 Jun 9;95(12):6693-8. doi: 10.1073/pnas.95.12.6693.
Histone H4 can be acetylated at N-terminal lysines K5, K8, K12, and K16, but newly synthesized H4 is diacetylated at K5/K12 in diverse organisms. This pattern is widely thought to be important for histone deposition onto replicating DNA. To investigate the importance of K5/K12 we have mutagenized these lysines in yeast and assayed for nucleosome assembly. Assaying was done in the absence of the histone H3 N terminus, which has functions redundant with those of H4 in histone deposition. Nucleosome assembly was assayed by three methods. Because nucleosome depletion may be lethal, we examined cell viability. We also analyzed nucleosome assembly in vivo and in vitro by examining plasmid superhelicity density in whole cells and supercoiling in yeast cell extracts. All three approaches demonstrate that mutagenizing K5 and K12 together does not prevent cell growth and histone deposition in vivo or in vitro. Therefore, K5/K12 cannot be required for nucleosome assembly in yeast. It is only when the first three sites of acetylation-K5, K8, and K12-are mutagenized simultaneously that lethality occurs and assembly is most strongly decreased both in vivo and in vitro. These data argue for the redundancy of sites K5, K8, and K12 in the deposition of yeast histone H4.
组蛋白H4可在N端赖氨酸K5、K8、K12和K16处发生乙酰化，但新合成的H4在多种生物体中在K5/K12处发生双乙酰化。人们普遍认为这种模式对于组蛋白沉积到复制的DNA上很重要。为了研究K5/K12的重要性，我们在酵母中对这些赖氨酸进行了诱变，并检测了核小体组装情况。检测是在没有组蛋白H3 N端的情况下进行的，组蛋白H3 N端在组蛋白沉积方面具有与H4冗余的功能。通过三种方法检测核小体组装。由于核小体耗竭可能是致命的，我们检测了细胞活力。我们还通过检测全细胞中的质粒超螺旋密度和酵母细胞提取物中的超螺旋来分析体内和体外的核小体组装。所有这三种方法都表明，同时诱变K5和K12不会阻止体内或体外的细胞生长和组蛋白沉积。因此，酵母中的核小体组装不需要K5/K12。只有当乙酰化的前三个位点——K5、K8和K12——同时被诱变时，才会出现致死性，并且体内和体外的组装都会最强烈地减少。这些数据表明酵母组蛋白H4沉积中K5、K8和K12位点具有冗余性。
