Nuclear Export of 60S Ribosomal Subunits Depends on Xpo1p and Requires a Nuclear Export Sequence-Containing Factor, Nmd3p, That Associates with the Large Subunit Protein Rpl10p

Abstract

Nuclear export of ribosomes requires a subset of nucleoporins and the Ran system, but specific transport factors have not been identified. Using a large subunit reporter (Rpl25p-eGFP), we have isolated several temperature-sensitive ribosomal export (rix) mutants. One of these corresponds to the ribosomal protein Rpl10p, which interacts directly with Nmd3p, a conserved and essential protein associated with 60S subunits. We find that thermosensitive nmd3 mutants are impaired in large subunit export. Strikingly, Nmd3p shuttles between the nucleus and cytoplasm and is exported by the nuclear export receptor Xpo1p. Moreover, we show that export of 60S subunits is Xpo1p dependent. We conclude that nuclear export of 60S subunits requires the nuclear export sequence-containing nonribosomal protein Nmd3p, which directly binds to the large subunit protein Rpl10p.

ACKNOWLEDGMENTS

We are grateful to C. Cole and A. Mutvei for the tsbank, J. Woolford for rpl16b-2, K. Weis forxpo1-1, and M. Rosbash for the LMB-sensitive xpo1strain. We especially thank Robin Reed for critical reading of the manuscript.

E.H. was recipient of grants from the Deutsche Forschungsgemeinschaft (Schwerpunktprogramm “Funktionelle Architektur des Zellkerns”), and O.G. holds an HFSP fellowship. D.T. was funded by the Wellcome Trust, and research from the Trumpower laboratory was supported by The Hitchcock Foundation and by NIH grant GM 20379.