The Role of Ded1 Binding to eIF4G1 in Yeast Translational Repression

Abstract

The translation of messenger RNA (mRNA) into proteins is a central process of all cells. The initiation of this process is highly orchestrated, involving many different players, such as initiation factors, helicases and the ribosome components. Ded1 is an RNA helicase and member of the DEAD-box RNA helicase family. This protein plays key roles in resolving 5' UTR secondary structures and recruiting ribosomal components. While Ded1’s role in translational initiation is well-studied, its role in translational repression during stress is unclear. Previous work has displayed that Ded1 physically interacts with the eukaryotic initiation factor 4G (eIF4G) in yeast, a protein serving as the nucleation point for the pre-initiation complex (PIC). Here, we report the creation of eIF4G1 mutants deleting the RNA-2 and RNA-3 domains of this protein, which have been reported binding sites for Ded1. Deletion of both domains failed to phenocopy ded1 mutants that displayed resistance to rapamycin, a drug that causes translational repression. We also show that eIF4G1 co-immunoprecipitates with Ded1 after deletion of these regions, but their interaction is weakened. Further, treatment with RNAse A indicates that the interaction between these two proteins is not RNA-mediated but is instead protein-protein binding. This suggests that eIF4G1's RNA-2 and RNA-3 domains are not the sole binding regions for Ded1 but are involved. Our results indicate that these mutations do not cause defects in translational repression and that the in vivo interaction of these two proteins may be more complex than the in vitro interactions observed.