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FEBS Lett. 2002 Sep 11;527(1-3):15-21.

Association of the mammalian proto-oncoprotein Int-6 with the three protein complexes eIF3, COP9 signalosome and 26S proteasome.

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Laboratoire de Biologie Moléculaire et Cellulaire, UMR5665-Centre National de la Recherche Scientifique, Ecole Normale Supérieure de Lyon, 46, Allée d'Italie, 69364 Cedex 07, Lyon, France


The mammalian Int-6 protein has been characterized as a subunit of the eIF3 translation initiation factor and also as a transforming protein when its C-terminal part is deleted. It includes a protein domain, which also exists in various subunits of eIF3, of the 26S proteasome and of the COP9 signalosome (CSN). By performing a two-hybrid screen with Int-6 as bait, we have isolated subunits belonging to all three complexes, namely eIF3-p110, Rpt4, CSN3 and CSN6. The results of transient expression experiments in COS7 cells confirmed the interaction of Int-6 with Rpt4, CSN3 and CSN6, but also showed that Int-6 is able to bind another subunit of the CSN: CSN7a. Immunoprecipitation experiments performed with the endogenous proteins showed that Int-6 binds the entire CSN, but in low amount, and also that Int-6 is associated with the 26S proteasome. Taken together these results show that the Int-6 protein can bind the three complexes with various efficiencies, possibly exerting a regulatory activity in both protein translation and degradation.

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