Promotes the eIF4F and eIF4A RNA-dependent ATP-hydrolysis activity with different efficiency depending on mRNAs, thus providing mRNA discrimination during initiation of translation. Homodimer (By similarity). Nonspherical monomer. mRNA-discriminating component of initiation complexes (PubMed:19493973). Phosphorylated. Belongs to the eIF-4 subunit B family. Truncated N-terminus.