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Mol. Cell. Biol. doi:10.1128/MCB.00738-08
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The poly(A)-binding protein-interacting protein 1 binds to eIF3 to stimulate translation

Department of Biochemistry, and McGill Cancer Centre, McGill University, 3655, promenade Sir William Osler, Montreal, Québec, Canada H3G 1Y6; Centro de Biologìa Molecular "Severo Ochoa"(CSIC-UAM), Facultad de Ciencias, Universidad Autõnoma de Madrid, Cantoblanco 28049 Madrid, Spain; Department of Biochemistry and Molecular Biology, University of Texas Medical School, Houston, Texas 77030, USA; RIKEN Systems and Structural Biology Center, Tsurumi-ku, Yokohama, Japan

^* To whom correspondence should be addressed. Email: nahum.sonenberg{at}mcgill.ca.

	Abstract

Poly(A)-binding protein (PABP) stimulates translation initiation by binding simultaneously to the mRNA poly(A) tail and eIF4G. PABP activity is regulated by PABP-interacting proteins (Paips). Paip1 binds PABP and stimulates translation by an unknown mechanism. Here, we describe the interaction between Paip1 and eIF3, which is direct, RNA-independent and mediated via the eIF3g (p44) subunit. Stimulation of translation by Paip1 in vivo was decreased upon deletion of the N-terminal sequence containing the eIF3-binding domain, and upon silencing of PABP or several eIF3 subunits. We also show the formation of ternary complexes composed of Paip1-PABP-eIF4G and Paip1-eIF3-eIF4G. Taken together, these data demonstrate that the eIF3-Paip1 interaction promotes translation. We propose that eIF3-Paip1 stabilizes the interaction between PABP and eIF4G, which brings about the circularization of the mRNA.