Environmental changes put stress on living organisms. We find that nutrient starvation induced dynamic protein aggregations in yeast cells, and many chaperones are involved in this process. Among them, Sti1/HOP, the co-chaperone of Hsp70 and Hsp90, plays roles in the formation of protein quality control (PQC) compartments and protein stasis (or proteostasis) maintenance, and it co-localizes to insoluble protein deposits (IPOD) by liquid-liquid phase separation (LLPS). Notably, the subcellular localization and cytoplasmic aggregation of Sti1 are rigorously regulated by the PQC machinery, including Ssa1/Hsp70 and Hsp82/Hsp90. On the other hand, STI1 deletion abolishes cytoplasmic aggregation of chaperones, including Ssa1, Hsp42 and Hsp104. These results reveal an interdependent model of chaperone-mediated aggregate formation. Furthermore, lysine 9 (K9) of Sti1 is identified as a critical residue governing its cytoplasmic condensation through a potential post-translational modification.
Chen et al. (Wed,) studied this question.