Genetics. Published Articles Ahead of Print: August 3, 2006, Copyright © 2006
doi:10.1534/genetics.106.062117


A more recent version of this article appeared on October 1, 2006.

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Ltv1 is required for efficient nuclear export of the ribosomal small subunit in S. cerevisiae

Robert M. Seiser 1, Alexandra E. Sundberg 2, Bethany J. Wollam 2, Pamela Zobel-Thropp 2, Katherine Baldwin 2, Maxwell D. Spector 2 and Deborah E. Lycan 2*

1 Roosevelt University
2 Lewis and Clark College

* To whom correspondence should be addressed. E-mail: lycan{at}lclark.edu.

Submitted on June 16, 2006
Revised on July 21, 2006
Accepted on 31 July 2006


Abstract

In eukaryotes, 40S and 60S ribosomal subunits are assembled in the nucleus and exported to the cytoplasm independently of one another. Nuclear export of the 60S requires the adapter protein Nmd3, but no analogous adapter has been identified for the 40S. Ltv1 is a non-essential, non-ribosomal protein that is required for 40S subunit biogenesis in yeast. Cells lacking LTV1 grow slowly, are hypersensitive to inhibitors of protein synthesis, and produce about half as many 40S subunits as do wild-type cells. Ltv1 interacts with Crm1, co-sediments in sucrose gradients with 43S/40S subunits, and co-purifies with late 43S particles. Here we show that Ltv1 can be both nuclear and cytoplasmic, that its nuclear export is Crm1-dependent and that it contains a functional NES that is sufficient to direct the export of an NLS-containing reporter. Small subunit export is reduced in {Delta}ltv1 mutants, as judged by an altered distribution of the 5' ITS1 rRNA and the 40S ribosomal protein, RpS3. Finally, we show a genetic interaction between LTV1 and YRB2, a gene that encodes a Ran-GTP-, Crm1-binding protein that facilitates small subunit export. We propose that Ltv1 functions as one of several possible adapter proteins that link the nuclear export machinery to the small subunit.

Key Words: LTV1, Ribosome biogenesis, YRB2, nuclear export, ribosomal protein S3




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