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Molecular and Cellular Biology, September 2008, p. 5348-5358, Vol. 28, No. 17
0270-7306/08/$08.00+0     doi:10.1128/MCB.02043-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Nuclear Export Receptor Xpo1/Crm1 Is Physically and Functionally Linked to the Spindle Pole Body in Budding Yeast ^,

Max Delbrück Centrum für Molekulare Medizin, Robert Rössle Strasse 10, 13092 Berlin, Germany,¹ Fachhochschule für Technik und Wirtschaft, Life Science Engineering, Blankenburger Pflasterweg 102, 13129 Berlin, Germany,² Medizinische Biochemie und Molekularbiologie, Universität des Saarlandes, 66421 Homburg, Germany³

Received 13 November 2007/ Returned for modification 28 December 2007/ Accepted 16 June 2008

The spindle pole body (SPB) represents the microtubule organizing center in the budding yeast Saccharomyces cerevisiae. It is a highly structured organelle embedded in the nuclear membrane, which is required to anchor microtubules on both sides of the nuclear envelope. The protein Spc72, a component of the SPB, is located at the cytoplasmic face of this organelle and serves as a receptor for the -tubulin complex. In this paper we show that it is also a binding partner of the nuclear export receptor Xpo1/Crm1. Xpo1 binds its cargoes in a Ran-dependent fashion via a short leucine-rich nuclear export signal (NES). We show that binding of Spc72 to Xpo1 depends on Ran-GTP and a functional NES in Spc72. Mutations in this NES have severe consequences for mitotic spindle morphology in vivo. This is also the case for xpo1 mutants, which show a reduction in cytoplasmic microtubules. In addition, we find a subpopulation of Xpo1 localized at the SPB. Based on these data, we propose a functional link between Xpo1 and the SPB and discuss a role for this exportin in spindle biogenesis in budding yeast.

Published ahead of print on 23 June 2008.

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