rDNA Condensation Promotes rDNA Separation from Nucleolar Proteins Degraded for Nucleophagy after TORC1 Inactivation

摘要

Nutrient starvation and inactivation of target of rapamycincomplex 1 (TORC1) protein kinase induce nucleophagypreferentially degrading only nucleolarcomponents in budding yeast. Nucleolar proteinsare relocated to sites proximal to the nucleus-vacuolejunction (NVJ), where micronucleophagy occurs,whereas rDNA, which is embedded in the nucleolusunder normal conditions, moves to NVJ-distal regions,causing rDNA dissociation from nucleolar proteinsafter TORC1 inactivation. This repositioningis mediated via chromosome linkage INM protein(CLIP)-cohibin complexes that tether rDNA to the innernuclear membrane. Here, we show that TORC1inactivation-induced rDNA condensation promotesthe 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 inactivationinducedrDNA condensation, compromised the repositioningand nucleophagic degradation of nucleolarproteins, although rDNA still escaped fromnucleophagic degradation in these mutants. We proposea model in which rDNA condensation afterTORC1 inactivation generates a motive force for therepositioning of rDNA and nucleolar proteins.