eIF-4B (eukaryotic translation initiation factor 4B),an RNA binding protein, is essential for the binding of mRNA to the 43S pre-initiation complex, which consists of the 40S ribosomal subunit bound to a ternary complex of eIF-2, GTP, and Met-tRNA stabilized by eIF-3. An arginine rich motif (ARM) in the carboxy-terminus of eIF-4B binds RNA non-specifically, while a canonical RNA motif (RMM) near the amino terminus binds specifically to 18S rRNA. The simultaneous binding of specific and nonspecific RNA may serve to facilitate the binding of the 40S subunit to the mRNA by serving as a bridge between the 18S rRNA and the mRNA. Besides its binding activity, eIF-4B in conjunction with eIF-4F, a heterotrimeric protein, stimulates the ATPase and RNA helicase activity of eIF-4E.