DDX3 is a member of the DEAD box family of proteins that possesses several conserved motifs which include the highly conserved DEAD (Asp-Glu-Ala-Asp) amino acid sequence motif. The major activity of DEAD box proteins is to function as ATP-dependent RNA helicases. As helicases, DEAD proteins play an important role in all aspects of RNA metabolism and function which include pre-mRNA splicing, RNA synthesis, RNA degradation, RNA export, RNA translation, RNA secondary structure formation, ribosome biogenesis, and the assembly of RNP complexes. DDX3 exhibits a variety of functions. DDX3 is a candidate tumor suppressor that suppresses tumor growth and transcriptionally activates the p21 promoter. DDX3 has been shown to play a role in translation as an eIF4E inhibitory protein that regulates translation initiation. These findings, as well as the observation that DDX3 is regulated by hepatitis C virus and is down-regulated in hepatocellular carcinoma, suggest an important role for DDX3 in growth-regulatory functions.