THE P20 AND DED1 PROTEINS HAVE ANTAGONISTIC ROLES IN EIFDE-DEPENDENT TRANSLATION IN SACCHAROMYCES-CEREVISIAE

The translation initiation factor eIF4E mediates the binding of the sm all ribosomal subunit to the cap structure at the 5' end of the mRNA. In Saccharomyces cerevisiae, the cap-binding protein eIF4E is mainly a ssociated with eIF4G, forming the cap-binding complex eIF4F. Other pro teins are detected upon purification of the complex on cap-affinity co lumns. Among them is p20, a protein of unknown function encoded by the C4F20 gene. Here, we show a negative regulatory role for the p20 prot ein 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 ph enotypes. Similar effects are observed for mutations in the DEDI gene, which we have isolated as a multicopy suppressor of a temperature-sen sitive eIF4E mutation. The DED1 gene encodes a putative RNA helicase o f the DEAD-box family. The analyses of its suppressor activity, of pol ysome profiles of ded1 mutant strains, and of synthetic lethal interac tions with different translation mutants indicate that the Ded1 protei n has a role in translation initiation in S. cerevisiae.