Graduate School of Science and Technology, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan.
Department of Science, Shizuoka University, Ohya 836, Suruga-ku, Shizuoka 422-8021, Japan.
Cell Rep. 2019 Sep 24;28(13):3423-3434.e2. doi: 10.1016/j.celrep.2019.08.059.
Nutrient starvation and inactivation of target of rapamycin complex 1 (TORC1) protein kinase induce nucleophagy preferentially degrading only nucleolar components in budding yeast. Nucleolar proteins are relocated to sites proximal to the nucleus-vacuole junction (NVJ), where micronucleophagy occurs, whereas rDNA, which is embedded in the nucleolus under normal conditions, moves to NVJ-distal regions, causing rDNA dissociation from nucleolar proteins after TORC1 inactivation. This repositioning is mediated via chromosome linkage INM protein (CLIP)-cohibin complexes that tether rDNA to the inner nuclear membrane. Here, we show that TORC1 inactivation-induced rDNA condensation promotes the repositioning of rDNA and nucleolar proteins. Defects in condensin, Rpd3-Sin3 histone deacetylase (HDAC), and high-mobility group protein 1 (Hmo1), which are involved in TORC1 inactivation-induced rDNA condensation, compromised the repositioning and nucleophagic degradation of nucleolar proteins, although rDNA still escaped from nucleophagic degradation in these mutants. We propose a model in which rDNA condensation after TORC1 inactivation generates a motive force for the repositioning of rDNA and nucleolar proteins.
营养饥饿和雷帕霉素靶蛋白复合物 1(TORC1)蛋白激酶失活诱导核噬作用,优先降解酿酒酵母中仅核仁成分。核仁蛋白被重定位到靠近核-液泡连接点(NVJ)的位置,在这里发生微核噬作用,而正常情况下嵌入核仁中的 rDNA 则移动到 NVJ 远端区域,导致 TORC1 失活后 rDNA 与核仁蛋白解离。这种重定位是通过染色体连接内膜蛋白(CLIP)-cohibin 复合物介导的,该复合物将 rDNA 固定在内核膜上。在这里,我们表明 TORC1 失活诱导的 rDNA 凝聚促进了 rDNA 和核仁蛋白的重定位。参与 TORC1 失活诱导的 rDNA 凝聚的 condensin、Rpd3-Sin3 组蛋白去乙酰化酶(HDAC)和高迁移率族蛋白 1(Hmo1)的缺陷,破坏了核仁蛋白的重定位和核噬作用降解,尽管在这些突变体中 rDNA 仍逃避核噬作用降解。我们提出了一个模型,即在 TORC1 失活后 rDNA 凝聚产生了 rDNA 和核仁蛋白重定位的动力。