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

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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 (m sup 7 GpppX) of the mRNA by the cap-binding complex eIF4F [1]. eIF4F is itself a three-subunit complex comprising the cap-binding protein eIF4E [2], eIF4A, an ATP-dependent RNA helicase [3], and eIF4G, which interacts with both eIF4A and eIF4E and enhances cap binding by eIF4E [4]. The mRNA 3' polyadenylate tail and the associated poly(A)-binding protein (PABP) also regulate translational initiation [5], probably by interacting with the 5' end of the mRNA [6,7]. In yeast [8,9] and plants [10], PABP interacts with eIF4G [8,9] but no such interaction has been reported in mammalian cells. Here, we describe a new human PABP-interacting protein, PAIP-1, 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.

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