Stress-induced translation inhibition through release of 40S scanning initiation factors

Cellular responses to environmental stress are frequently mediated by RNA-binding proteins (RBPs). Here, we examined global RBP dynamics in Saccharomyces cerevisiae in response to glucose starvation and heat shock. Each stress induced rapid remodeling of the protein:RNA interactome, without corresponding changes in RBP abundance. Consistent with translational shutdown, ribosomal proteins contacting the mRNA showed decreased RNA-association. Among translation components, in either stress RNA-association was most reduced for initiation factors involved in 40S scanning (eIF4A, eIF4B, and Ded1), indicating common mechanisms of translational repression. In unstressed cells, eIF4A, eIF4B, and Ded1 primarily targeted the 5′-ends of mRNAs. Following glucose withdrawal, mRNAs remained stable, but 5’-binding was abolished within 30sec, explaining the rapid translation shutdown. Heat shock induced progressive loss of 5’ RNA-binding by initiation factors over ~16min. Translation shutoff provoked 5’-degradation by Xrn1, selectively for mRNAs encoding translation-related factors. These results reveal mechanisms underlying translational control of gene expression during stress.