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Vol. 18, Issue 9, 3692-3708, September 2007

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Multiple Conserved Domains of the Nucleoporin Nup124p and Its Orthologs Nup1p and Nup153 Are Critical for Nuclear Import and Activity of the Fission Yeast Tf1 Retrotransposon

Laboratory of Nucleopore Biology, Institute of Molecular and Cell Biology, Singapore 138673

Submitted December 1, 2006; Revised June 18, 2007; Accepted June 26, 2007
Monitoring Editor: Susan Wente

The nucleoporin Nup124p is a host protein required for the nuclear import of both, retrotransposon Tf1-Gag as well as the retroviral HIV-1 Vpr in fission yeast. The human nucleoporin Nup153 and the Saccharomyces cerevisiae Nup1p were identified as orthologs of Nup124p. In this study, we show that all three nucleoporins share a large FG/FXFG-repeat domain and a C-terminal peptide sequence, GRKIxxxxxRRKx, that are absolutely essential for Tf1 retrotransposition. Though the FXFG domain was essential, the FXFG repeats themselves could be eliminated without loss of retrotransposon activity, suggesting the existence of a common element unrelated to FG/FXFG motifs. The Nup124p C-terminal peptide, GRKIAVPRSRRKR, was extremely sensitive to certain single amino acid changes within stretches of the basic residues. On the basis of our comparative study of Nup124p, Nup1p, and Nup153 domains, we have developed peptides that specifically knockdown retrotransposon activity by disengaging the Tf1-Gag from its host nuclear transport machinery without any harmful consequence to the host itself. Our results imply that those domains challenged a specific pathway affecting Tf1 transposition. Although full-length Nup1p or Nup153 does not complement Nup124p, the functionality of their conserved domains with reference to Tf1 activity suggests that these three proteins evolved from a common ancestor.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

* These authors contributed equally to this work.

Address correspondence to: David Balasundaram (davidb{at}imcb.a-star.edu.sg).