Interaction of polyadenylate-binding protein with the eIF4G homologue PAIP enhances translation

In the initiation of translation in eukaryotes, binding of the small ribosomal subunit to the messenger RNA results from recognition of the 5' cap structure (m7GpppX) of the mRNA by the cap-binding complex eIF4F. eIF4F is itself a three-subunit complex comprising the cap-binding protein eIF4E, eIF4A, an ATP-dependent RNA helicase, and eIF4G, which interacts with both eIF4A and eIF4E and enhances cap binding by eIF4E. The mRNA 3' polyadenylate tail and the associated poly(A)-binding protein (PABP) also regulate translational initiation, probably by interacting with the 5' end of the mRNA. In yeast and plants, PABP interacts with eIF4G but no such interaction has been reported in mammalian cells. Here, we describe a new human PABP-interacting protein, PAIP-I, whose sequence is similar to the central portion of eIF4G and which interacts with eIF4A. Overexpression of PAIP-1 in COS-7 cells stimulates translation, perhaps by providing a physical link between the mRNA termini.