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Cells fine-tune microtubule assembly in both space and time to give rise to distinct edifices with specific cellular functions. In proliferating cells, microtubules are highly dynamics, and proliferation cessation often leads to their stabilization. One of the most stable microtubule structures identified to date is the nuclear bundle assembled in quiescent yeast. In this article, we characterize the original multistep process driving the assembly of this structure. This Aurora B-dependent mechanism follows a precise temporality that relies on the sequential actions of kinesin-14, kinesin-5, and involves both microtubule–kinetochore and kinetochore–kinetochore interactions. Upon quiescence exit, the microtubule bundle is disassembled via a cooperative process involving kinesin-8 and its full disassembly is required prior to cells re-entry into proliferation. Overall, our study provides the first description, at the molecular scale, of the entire life cycle of a stable microtubule structure in vivo and sheds light on its physiological function. 

Coenzyme Q (CoQ) is an essential redox-active lipid that plays a major role in the electron transport chain, driving mitochondrial ATP synthesis. In Saccharomyces cerevisiae (yeast), CoQ biosynthesis occurs exclusively in the mitochondrial matrix via a large protein-lipid complex, the CoQ synthome, comprised of CoQ itself, late-stage CoQ-intermediates, and the polypeptides Coq3-Coq9 and Coq11. Coq11 is suggested to act as a negative modulator of CoQ synthome assembly and CoQ synthesis, as its deletion enhances Coq polypeptide content, produces an enlarged CoQ synthome, and restores respiration in mutants lacking the CoQ chaperone polypeptide, Coq10. The CoQ synthome resides in specific niches within the inner mitochondrial membrane, termed CoQ domains, that are often located adjacent to the endoplasmic reticulum-mitochondria encounter structure (ERMES). Loss of ERMES destabilizes the CoQ synthome and renders CoQ biosynthesis less efficient. Here we show that deletion of COQ11 suppresses the respiratory deficient phenotype of select ERMES mutants, results in repair and reorganization of the CoQ synthome, and enhances mitochondrial CoQ domains. Given that ER-mitochondrial contact sites coordinate CoQ biosynthesis, we used a Split-MAM (Mitochondrial Associated Membrane) artificial tether consisting of an ER-mitochondrial contact site reporter, to evaluate the effects of artificial membrane tethers on CoQ biosynthesis in both wild-type and ERMES mutant yeast strains. Overall, this work identifies the deletion of COQ11 as a novel suppressor of phenotypes associated with ERMES deletion mutants and indicates that ER-mitochondria tethers influence CoQ content and turnover, highlighting the role of membrane contact sites in regulating mitochondrial respiratory homeostasis.