Department of Biomolecular Chemistry and Laboratory of Genetics, School of Medicine and Public Health and College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI 53706, USA.
Proc Natl Acad Sci U S A. 2011 Aug 30;108(35):14572-7. doi: 10.1073/pnas.1105262108. Epub 2011 Aug 15.
The posttranslational addition of palmitate to cysteines occurs ubiquitously in eukaryotic cells, where it functions in anchoring target proteins to membranes and in vesicular trafficking. Here we show that the Saccharomyces cerevisiae palmitoyltransferase Pfa4 enhanced heterochromatin formation at the cryptic mating-type loci HMR and HML via Rif1, a telomere regulatory protein. Acylated Rif1 was detected in extracts from wild-type but not pfa4Δ mutant cells. In a pfa4Δ mutant, Rif1-GFP dispersed away from foci positioned at the nuclear periphery into the nucleoplasm. Sir3-GFP distribution was also perturbed, indicating a change in the nuclear dynamics of heterochromatin proteins. Genetic analyses indicated that PFA4 functioned upstream of RIF1. Surprisingly, the pfa4Δ mutation had only mild effects on telomeric regulation, suggesting Rif1's roles at HM loci and telomeres were more complexly related than previously thought. These data supported a model in which Pfa4-dependent palmitoylation of Rif1 anchored it to the inner nuclear membrane, influencing its role in heterochromatin dynamics.
在真核细胞中，半胱氨酸的翻译后棕榈酰化普遍存在，其功能是将靶蛋白锚定到膜上，并参与囊泡运输。在这里，我们发现酿酒酵母的棕榈酰转移酶 Pfa4 通过端粒调节蛋白 Rif1 增强了隐型交配型位点 HMR 和 HML 上的异染色质形成。在野生型细胞提取物中检测到了酰化的 Rif1，但在 pfa4Δ 突变体细胞中却没有。在 pfa4Δ 突变体中， Rif1-GFP 从定位于核周的焦点分散到核质中。Sir3-GFP 的分布也受到干扰，表明异染色质蛋白的核动态发生了变化。遗传分析表明，PFA4 在前 Rif1 发挥作用。令人惊讶的是，pfa4Δ 突变对端粒调控的影响很小，这表明 Rif1 在 HM 位点和端粒上的作用比之前认为的更为复杂。这些数据支持了这样一个模型，即 Pfa4 依赖的 Rif1 棕榈酰化将其锚定在内核膜上，影响其在异染色质动力学中的作用。
