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首页> 外文期刊>Molecular and Cellular Biology >Yeast Chromatin Assembly Complex 1 Protein Excludes Nonacetylatable Forms of Histone H4 from Chromatin and the Nucleus
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Yeast Chromatin Assembly Complex 1 Protein Excludes Nonacetylatable Forms of Histone H4 from Chromatin and the Nucleus

机译：酵母染色质装配体1蛋白排除了染色质和细胞核中组蛋白H4的非乙酰化形式

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In yeast, the establishment and maintenance of a transcriptionally silent chromatin state are dependent upon the acetylation state of the N terminus of histone proteins. Histone H4 proteins that contain mutations in N-terminal lysines disrupt heterochromatin and result in yeast that cannot mate. Introduction of a wild-type copy of histone H4 restores mating, despite the presence of the mutant protein, suggesting that mutant H4 protein is either excluded from, or tolerated in, chromatin. To understand how the cell differentiates wild-type histone and mutant histone in which the four N-terminal lysines were replaced with alanine (H4-4A), we analyzed silencing, growth phenotypes, and the histone composition of chromatin in yeast strains coexpressing equal amounts of wild-type and mutant H4 proteins (histone H4 heterozygote). We found that histone H4 heterozygotes have defects in heterochromatin silencing and growth, implying that mutations in H4 are not completely recessive. Nuclear preparations from histone H4 heterozygotes contained less mutant H4 than wild-type H4, consistent with the idea that cells exclude some of the mutant histone. Surprisingly, the N-terminal nuclear localization signal of H4-4A fused to green fluorescent protein was defective in nuclear localization, while a mutant in which the four lysines were replaced with arginine (H4-4R) appeared to have normal nuclear import, implying a role for the charged state of the acetylatable lysines in the nuclear import of histones. The biased partial exclusion of H4-4A was dependent upon Cac1p, the largest subunit of yeast chromatin assembly factor 1 (CAF-1), as well as upon the karyopherin Kap123p, but was independent of Cac2p, another CAF-1 component, and other chromatin assembly proteins (Hir3p, Nap1p, and Asf1p). We conclude that N-terminal lysines of histone H4 are important for efficient histone nuclear import. In addition, our data support a model whereby Cac1p and Kap123 cooperate to ensure that only appropriately acetylated histone H4 proteins are imported into the nucleus.
机译：在酵母中，转录沉默染色质状态的建立和维持取决于组蛋白N末端的乙酰化状态。在N端赖氨酸中含有突变的组蛋白H4蛋白破坏了异染色质，导致酵母无法交配。尽管存在突变蛋白，引入组蛋白H4的野生型副本仍可恢复交配，这表明突变H4蛋白被排除在染色质之外，或被染色质所耐受。为了了解细胞如何区分野生型组蛋白和突变组蛋白（其中四个N端赖氨酸被丙氨酸（H4-4A）取代），我们分析了共表达相同量酵母菌株中染色质的沉默，生长表型和组蛋白组成类型的野生型和突变型H4蛋白（组蛋白H4杂合子）。我们发现，组蛋白H4杂合子在异染色质沉默和生长中存在缺陷，这暗示H4中的突变不是完全隐性的。组蛋白H4杂合子的核制品所含突变体H4比野生型H4少，这与细胞排除某些突变组蛋白的想法是一致的。令人惊讶的是，与绿色荧光蛋白融合的H4-4A的N端核定位信号在核定位中是有缺陷的，而一个突变体，其中四个赖氨酸被精氨酸（H4-4R）取代，似乎具有正常的核输入，这意味着乙酰化赖氨酸的带电状态在组蛋白核输入中的作用。 H4-4A的部分偏倚取决于酵母染色质装配因子1（CAF-1）的最大亚基Cac1p，以及核蛋白Kap123p，但不依赖于Cac2p，另一种CAF-1成分和其他染色质装配蛋白（Hir3p，Nap1p和Asf1p）。我们得出结论，组蛋白H4的N端赖氨酸对于有效的组蛋白核导入很重要。此外，我们的数据支持Cac1p和Kap123合作以确保仅将适当乙酰化的组蛋白H4蛋白导入细胞核的模型。

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