The ribosome-associated chaperone Zuo1 controls translation upon TORC1 inhibition

Eukaryotic cells achieve proteostasis by ensuring their protein requirements are met through tight control of TORC1 activity. 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.