ATP-binding RNA helicase involved in translation initiation. Part of the 43S pre-initiation complex that is required for efficient initiation on mRNAs of higher eukaryotes with structured 5'-UTRs by promoting efficient NTPase-dependent 48S complex formation. Specifically binds to the 40S ribosome near the mRNA entrance. Does not possess a processive helicase activity. ATP + H2O = ADP + H(+) + phosphate Part of the 43S pre-initiation complex (PIC). Belongs to the DEAD box helicase family. DEAH subfamily.