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J. Biol. Chem., Vol. 281, Issue 26, 18227-18235, June 30, 2006

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The Multi-KH Domain Protein of Saccharomyces cerevisiae Scp160p Contributes to the Regulation of Telomeric Silencing^*

Francesc-Xavier Marsellach¹, Dori Huertas², and Fernando Azorín³

From the Departament de Biologia Molecular i Cellular, Institut de Biologia Molecular de Barcelona (IBMB), Consejo Superior de Investigaciones Científicas, Parc Científic de Barcelona, 08028 Barcelona, Spain and the Institut de Recerca Biomèdica (IRB), Parc Científic de Barcelona, 08028 Barcelona, Spain

Multi-KH domain proteins are highly evolutionarily conserved proteins that associate to polyribosomes and participate in RNA metabolism. Recent evidence indicates that multi-KH domain proteins also contribute to the structural organization of heterochromatin both in mammals and Drosophila. Here, we show that the multi-KH domain protein of Saccharomyces cerevisiae, Scp160p, contributes to silencing at telomeres and at the mating-type locus, but not to ribosomal silencing. The contribution of Scp160p to silencing is independent of its binding to the ribosome as deletion of the last two KH domains, which mediate ribosomal binding, has no effect on silencing. Disruption of SCP160 increases cell ploidy but this effect is also independent of the contribution of Scp160p to telomeric silencing as strong relief of silencing is observed in scp160 cells with normal ploidy and, vice versa, scp160 cells with highly increased ploidy show no significant silencing defects. The TPE phenotype of scp160 cells associates to a decreased Sir3p deposition at telomeres and, in good agreement, silencing is rescued by SIR3 overexpression and in a rif1rif2 mutant. Scp160p shows a distinct perinuclear localization that is independent of its ability to bind ribosomes. Moreover, telomere clustering at the nuclear envelope is perturbed in scp160 cells and disruption of the histone deacetylase RPD3, which is known to improve telomere clustering, rescues telomeric silencing in scp160 cells. These results are discussed in the context of a model in which Scp160p contributes to silencing by helping telomere clustering.

Received for publication, February 22, 2006 , and in revised form, April 20, 2006.

^* This work was supported by Grants from the MCyT (BMC2003-243), the CIRIT (2001SGR00344), and the EU (LSHB-CT-2004-511965). 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.

¹ Receipt of a doctoral fellowship from CIRIT.

² Receipt of an I3P postdoctoral contract of CSIC.

³ To whom correspondence should be addressed: Departament de Biologia Molecular i Cellular, Institut de Biologia Molecular de Barcelona, CSIC, Parc Científic de Barcelona, Josep Samitier, 1-5.08028 Barcelona, Spain. Tel.: 3493-403-4958; Fax: 3493-403-4979; E-mail: fambmc{at}ibmb.csic.es.

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