Yeast Uri1p promotes translation initiation and may provide a link to cotranslational quality control

Translation initiation in eukaryotes is accomplished by a large set of translation initiation factors, some of which are regulated by signals monitoring intracellular and environmental conditions. Here, we show that Uri1p is required for efficient translation initiation in budding yeast. Indeed, uri1Delta cells are slow growing, sensitive to translation inhibitors and they exhibit an increased 80S peak in polysome profiles. Moreover, GCN4 translation is derepressed in uri1Delta cells, strongly supporting an initiation defect. Genetic and biochemical experiments indicate that Uri1p interacts with the translation initiation factor eIF1A and promotes ternary complex (TC) recruitment to the 40S subunit. Interestingly, we found that Uri1p is also part of a chaperone-network, including the prefoldin Pfd6p and several other proteins involved in cotranslational quality control such as the ribosome-associated Hsp70 chaperone Ssb1p, the Hsp40 Sis1p and the translation elongation factor eEF1A. Together with genetic data, these interactions indicate that Uri1p may coordinate translation initiation and cotranslational quality control.