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J. Biol. Chem., Vol. 282, Issue 52, 37389-37401, December 28, 2007

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CPEB Interacts with an Ovary-specific eIF4E and 4E-T in Early Xenopus Oocytes^*

Nicola Minshall, Marie Helene Reiter, Dominique Weil, and Nancy Standart¹

From the Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, United Kingdom and CNRS-FRE 2937, Institut Andre Lwoff, Villejuif 94801, France

CPEB (cytoplasmic polyadenylation element-binding protein) is an important regulator of translation in oocytes and neurons. Although previous studies of CPEB in late Xenopus oocytes involve the eIF4E-binding protein maskin as the key factor for the repression of maternal mRNA, a second mechanism must exist, since maskin is absent earlier in oogenesis. Using co-immunoprecipitation and gel filtration assays, we show that CPEB specifically interacts, via protein/protein interactions, with the RNA helicase Xp54, the RNA-binding proteins P100(Pat1) and RAP55, the eIF4E-binding protein 4E-T, and an eIF4E protein. Remarkably, these CPEB complex proteins have been characterized, in one or more organism, as P-body, maternal, or neuronal granule components. We do not detect interactions with eIF4E1a, the canonical cap-binding factor, eIF4G, or eIF4A or with proteins expressed late in oogenesis, including maskin, PARN, and 4E-BP1. The eIF4E protein was identified as eIF4E1b, a close homolog of eIF4E1a, whose expression is restricted to oocytes and early embryos. Although eIF4E1b possesses all residues required for cap and eIF4G binding, it binds m⁷GTP weakly, and in pull-down assays, rather than binding eIF4G, it binds 4E-T, in a manner independent of the consensus eIF4E-binding site, YSKEELL. Wild type and Y-A mutant 4E-T (which binds eIF4E1b but not eIF4E1a), when tethered to a reporter mRNA, represses its translation in a cap-dependent manner, and injection of eIF4E1b antibody accelerates meiotic maturation. Altogether, our data suggest that CPEB, partnered with several highly conserved RNA-binding partners, inhibits protein synthesis in oocytes using a novel pairing of 4E-T and eIF4E1b.

Received for publication, June 5, 2007 , and in revised form, October 16, 2007.

^* This work was supported by the Wellcome Trust and the Biotechnology and Biological Sciences Research Council (to N. S.) and La Ligue Nationale contre le Cancer (to D. W.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Table 1 and Figs. S1–S4.

¹ To whom correspondence should be addressed. Fax: 44-1223-760-002; E-mail: nms{at}mole.bio.cam.ac.uk.

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