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During early development, control of the poly(A) tail length by cytoplas-mic polyadenylation is critical for the regulation of specific mRNA expres-sion. Gld2, an atypical poly(A) polymerase, is involved in cytoplasmic polyadenylation inXenopusoocytes. In this study, a new XGld2-interacting protein was identified:XenopusRNA-binding motif protein 9 (XRbm9). | ễFEBS Journal Xenopus Rbm9 is a novel interactor of XGld2 in the cytoplasmic polyadenylation complex Catherine Papin Christel Rouget and Elisabeth Mandart Centre de Recherche en Biochimie Macromoleculaire Universite Montpellier II France Keywords cytoplasmic polyadenylation Gld2 poly A polymerase Rbm9 Xenopus oocyte Correspondence C. Papin Centre de Recherche en Biochimie Macromoleculaire UMR 5237 Universite Montpellier II CNRS 1919 Route de Mende 34293 Montpellier Cedex 5 France Fax 33 4 99 61 99 01 Tel 33 4 99 61 99 59 E-mail catherine.papin@igh.cnrs.fr E. Mandart Centre de Recherche en Biochimie Macromoleculaire UMR 5237 Universite Montpellier II CNRS 1919 Route de Mende 34293 Montpellier Cedex 5 France Fax 33 467 521559 Tel 33 467 613339 E-mail elisabeth.mandart@crbm.cnrs.fr During early development control of the poly A tail length by cytoplasmic polyadenylation is critical for the regulation of specific mRNA expression. Gld2 an atypical poly A polymerase is involved in cytoplasmic polyadenylation in Xenopus oocytes. In this study a new XGld2-interacting protein was identified Xenopus RNA-binding motif protein 9 XRbm9 . This RNA-binding protein is exclusively expressed in the cytoplasm of Xenopus oocytes and interacts directly with XGld2. It is shown that XRbm9 belongs to the cytoplasmic polyadenylation complex together with cytoplasmic polyadenylation element-binding protein CPEB cleavage and polyadenylation specificity factor CPSF and XGld2. In addition tethered XRbm9 stimulates the translation of a reporter mRNA. The function of XGld2 in stage VI oocytes was also analysed. The injection of XGld2 antibody into oocytes inhibited polyadenylation showing that endogenous XGld2 is required for cytoplasmic polyadenylation. Unexpectedly XGld2 and CPEB antibody injections also led to an acceleration of meiotic maturation suggesting that XGld2 is part of a masking complex with CPEB and is associated with repressed mRNAs in oocytes. Present address Regulation des ARNm