Yeast Ran-Binding Protein 1 (Yrb1) Shuttles between the Nucleus and Cytoplasm and Is Exported from the Nucleus via a CRM1(XPO1)-Dependent Pathway

Abstract

The RanGTP-binding protein RanBP1, which is located in the cytoplasm, has been implicated in release of nuclear export complexes from the cytoplasmic side of the nuclear pore complex. Here we show that Yrb1 (the yeast homolog of RanBP1) shuttles between the nucleus and the cytoplasm. Nuclear import of Yrb1 is a facilitated process that requires a short basic sequence within the Ran-binding domain (RBD). By contrast, nuclear export of Yrb1 requires an intact RBD, which forms a ternary complex with the Xpo1 (Crm1) NES receptor in the presence of RanGTP. Nuclear export of Yrb1, however, is insensitive towards leptomycin B, suggesting a novel type of substrate recognition between Yrb1 and Xpo1. Taken together, these data suggest that ongoing nuclear import and export is an important feature of Yrb1 function in vivo.

ACKNOWLEDGMENTS

Special thanks go to D. Lau for technical support, D. Zenklusen (Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland) for sharing unpublished results, B. Wolff (Novartis Research Institute, Vienna, Austria) for leptomycin B, and J. Thorner (University of California, Berkeley), for generous support. We thank K. Weis (University of California, Berkeley), I. Macara (Markey Center for Cell Signaling, Charlottesville, Va.), M. Rosbash (M. Neville) and L. Davis (Brandeis University, Waltham, Mass.), M. Nomura (University of California, Irvine), M. Fitzgerald-Hayes (University of Massachusetts, Amherst), and G. Stier and S. Labeit (EMBL, Heidelberg, Germany) for providing us with strains and plasmids. We are grateful to G. Simos and O. Gadal for critical reading of the manuscript.

M.K. is a recipient of grants from the Deutsche Forschungsgemeinschaft (Ku 1235/1-1) and is supported by a fellowship provided by the Swiss National Research Foundation.