Marsellach Francesc-Xavier, Huertas Dori, Azorín Fernando
Departament de Biologia Molecular i Cellular, Institut de Biologia Molecular de Barcelona (IBMB), Consejo Superior de Investigaciones Científicas, Parc Científic de Barcelona, Josep Samitier 1-5, 08028 Barcelona, Spain.
J Biol Chem. 2006 Jun 30;281(26):18227-35. doi: 10.1074/jbc.M601671200. Epub 2006 Apr 21.
Multi-KH domain proteins are highly evolutionarily conserved proteins that associate to polyribosomes and participate in RNA metabolism. Recent evidence indicates that multi-KH domain proteins also contribute to the structural organization of heterochromatin both in mammals and Drosophila. Here, we show that the multi-KH domain protein of Saccharomyces cerevisiae, Scp160p, contributes to silencing at telomeres and at the mating-type locus, but not to ribosomal silencing. The contribution of Scp160p to silencing is independent of its binding to the ribosome as deletion of the last two KH domains, which mediate ribosomal binding, has no effect on silencing. Disruption of SCP160 increases cell ploidy but this effect is also independent of the contribution of Scp160p to telomeric silencing as strong relief of silencing is observed in Deltascp160 cells with normal ploidy and, vice versa, Deltascp160 cells with highly increased ploidy show no significant silencing defects. The TPE phenotype of Deltascp160 cells associates to a decreased Sir3p deposition at telomeres and, in good agreement, silencing is rescued by SIR3 overexpression and in a Deltarif1Deltarif2 mutant. Scp160p shows a distinct perinuclear localization that is independent of its ability to bind ribosomes. Moreover, telomere clustering at the nuclear envelope is perturbed in Deltascp160 cells and disruption of the histone deacetylase RPD3, which is known to improve telomere clustering, rescues telomeric silencing in Deltascp160 cells. These results are discussed in the context of a model in which Scp160p contributes to silencing by helping telomere clustering.
多KH结构域蛋白是高度进化保守的蛋白，与多核糖体结合并参与RNA代谢。最近的证据表明，多KH结构域蛋白在哺乳动物和果蝇中也有助于异染色质的结构组织。在这里，我们表明酿酒酵母的多KH结构域蛋白Scp160p有助于端粒和交配型位点的沉默，但对核糖体沉默没有作用。Scp160p对沉默的贡献与其与核糖体的结合无关，因为介导核糖体结合的最后两个KH结构域的缺失对沉默没有影响。SCP160的破坏会增加细胞倍性，但这种效应也与Scp160p对端粒沉默的贡献无关，因为在倍性正常的Deltascp160细胞中观察到沉默的强烈缓解，反之亦然，倍性高度增加的Deltascp160细胞没有明显的沉默缺陷。Deltascp160细胞的TPE表型与端粒处Sir3p沉积减少有关，并且与此一致，通过SIR3过表达和在Deltarif1Deltarif2突变体中可以挽救沉默。Scp160p显示出独特的核周定位，这与其结合核糖体的能力无关。此外，Deltascp160细胞中核膜处的端粒聚集受到干扰，并且已知可改善端粒聚集的组蛋白脱乙酰酶RPD3的破坏可挽救Deltascp160细胞中的端粒沉默。这些结果在一个模型的背景下进行了讨论，在该模型中，Scp160p通过帮助端粒聚集来促进沉默。
