ATP-dependent RNA helicase. Core component of the splicing-dependent multiprotein exon junction complex (EJC) deposited at splice junctions on mRNAs. The EJC is a dynamic structure consisting of core proteins and several peripheral nuclear and cytoplasmic associated factors that join the complex only transiently either during EJC assembly or during subsequent mRNA metabolism. The EJC marks the position of the exon-exon junction in the mature mRNA for the gene expression machinery and the core components remain bound to spliced mRNAs throughout all stages of mRNA metabolism thereby influencing downstream processes including nuclear mRNA export, subcellular mRNA localization, translation efficiency and nonsense-mediated mRNA decay (NMD). Its RNA-dependent ATPase and RNA-helicase activities are induced by MLN51/CASC3, but abolished in presence of the MAGO-Y14 heterodimer, thereby trapping the ATP-bound EJC core onto spliced mRNA in a stable conformation. The inhibition of ATPase activity by the MAGO-Y14 heterodimer increases the RNA-binding affinity of the EJC (By similarity). Plays a role in abiotic stress adaptation. Can regulate abiotic stress resistance partially via the control of acetoacetyl-CoA thiolase 2 (AC Q8S4Y1) expression (PubMed:26883227). (Microbial infection) Functions as host RNA helicase that is co-opted by the tombusvirus (TBSV) RNA replication enhancer to greatly enhance tombusvirus replication. Interacts with the viral minus-strand RNA and the replication proteins within the viral replicase. ATP + H2O = ADP + H(+) + phosphate Interacts with ALY4 (PubMed:19435936). Interacts with MAGO (PubMed:26867216). Interacts with CPL1/FRY2 (PubMed:26887918). Hypoxia causes transition from diffuse nucleoplasmic localization to accumulation in speckles in nuclei of root cells (PubMed:19435936). Localized to the nucleus when hypophosphorylated. Hyperphosphorylation of EIF4A3 increases its cytoplasmic localization (PubMed:26887918). Nucleocytoplasmic shuttling protein. Travels to the cytoplasm as part of the exon junction complex (EJC) bound to mRNA (By similarity). Induced by cold and heat stresses. The Q motif is unique to and characteristic of the DEAD box family of RNA helicases and controls ATP binding and hydrolysis. Phosphorylated at Ser-100 and Ser-101. Phosphorylation status of Ser-100 and Ser-101 largely determines the subcellular localization of EIF4A3. No visible phenotype under normal growth conditions, but mutant seedlings show increased sensitivity to cold and heat stresses. Belongs to the DEAD box helicase family. DDX48/FAL1 subfamily. Truncated N-terminus.