Abstract
The translation initiation factor eIF4E mediates the binding of the small ribosomal subunit to the cap structure at the 5' end of the mRNA. In Saccharomyces cerevisiae, the cap-binding protein eIF4E is mainly associated with eIF4G, forming the cap-binding complex eIF4F. Other proteins are detected upon purification of the complex on cap-affinity columns. Among them is p20, a protein of unknown function encoded by the CAF20 gene. Here, we show a negative regulatory role for the p20 protein in translation initiation. Deletion of CAF20 partially suppresses mutations in translation initiation factors. Overexpression of the p20 protein results in a synthetic enhancement of translation mutation phenotypes. Similar effects are observed for mutations in the DED1 gene, which we have isolated as a multicopy suppressor of a temperature-sensitive eIF4E mutation. The DED1 gene encodes a putative RNA helicase of the DEAD-box family. The analyses of its suppressor activity, of polysome profiles of ded1 mutant strains, and of synthetic lethal interactions with different translation mutants indicate that the Ded1 protein has a role in translation initiation in S. cerevisiae.