Identification of Zuo1 interactors upon rapamycin stress

Proteostasis is tightly regulated by TORC1 to meet cellular requirements. Upon TORC1 inhibition, degradative activity is increased, and protein synthesis is reduced through inhibition of translation initiation, to maintain cell viability. Here, we show that the ribosome-associated complex (RAC)/Ssb chaperone system is required to maintain proteostasis and cell viability under TORC1 inhibition, in yeast. In the absence of the Hsp40 cochaperone Zuo1, translation does not decrease in response to loss of TORC1 activity. The functional interaction between Zuo1 and its Hsp70 partner, Ssb is required for proper translational control and proteostasis maintenance upon TORC1 inhibition. Further, we have found that the rapid degradation of eIF4G following TORC1 inhibition is prevented in zuo1Δ cells, contributing to decreased survival in these conditions. Our findings suggest a new role for RAC/Ssb in regulating translation in response to changes in TORC1 signalling.