The DEAD-Box RNA helicase family is a conserved group of enzymes that function in gene expression through ATP-dependent RNA unwinding and ribonucleoprotein (RNP) remodeling. DEAD-Box helicases function in multiple cellular processes, including pre-mRNA processing, translation, mRNA export, and mRNA decay. Although DEAD-Box proteins are critical for gene expression, much of their mechanistic activities are poorly understood. DEAD-Box proteins have increasingly been linked to tumorigenesis in humans, and better defining their activity at the mechanistic level will aid in understanding the underlying disease pathology. In this study, we used the model organism Saccharomyces cerevisiae to study the human DEAD-Box protein DDX3 orthologue, Ded1, and its role in translation initiation during cellular stress. Recently, we have found that Ded1 is an important mediator of the cellular stress response in a TOR-dependent manner. TOR regulates protein synthesis dependent on energy availability in the cell by regulating the assembly of the eukaryotic translation initiation complex. Human DDX3 has been found to interact with translation initiation complex subunit eIF4E and Ded1 has been found to interact with the translation initiation complex subunit eIF4G. In this study, we examined the purported interaction region between Ded1 and eIF4G on the C-terminus of Ded1 and found that ded1 Δ591-604 prevents eIF4G degradation under rapamycin treatment and confers resistance to rapamycin-induced growth inhibition. We also examined putative regulatory phosphorylation sites in the purported Ded1 eIF4G binding region. We propose that the Ded1/eIF4G interaction is critical for the repression of translation by Ded1 and that eIF4G degradation may be regulated by Ded1 under stress conditions.

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