Yrb4p, a yeast Ran-GTP-binding protein involved in import of ribosomal protein L25 into the nucleus

Abstract

Gsp1p, the essential yeast Ran homologue, is a key regulator of transport across the nuclear pore complex (NPC). We report the identification of Yrb4p, a novel Gsp1p binding protein. The 123 kDa protein was isolated from Saccharomyces cerevisiae cells and found to be related to importin-β, the mediator of nuclear localization signal (NLS)-dependent import into the nucleus, and to Pse1p. Like importin-β, Yrb4p and Pse1p specifically bind to Gsp1p-GTP, protecting it from GTP hydrolysis and nucleotide exchange. The GTPase block of Gsp1p complexed to Yrb4p or Pse1p is released by Yrb1p, which contains a Gsp1p binding domain distinct from that of Yrb4p. This might reflect an in vivo function for Yrb1p. Cells disrupted for YRB4 are defective in nuclear import of ribosomal protein L25, but show no defect in the import of proteins containing classical NLSs. Expression of a Yrb4p mutant deficient in Gsp1p-binding is dominantlethal and blocks bidirectional traffic across the NPC in wild-type cells. L25 binds to Yrb4p and Pse1p and is released by Gsp1p-GTP. Consistent with its putative role as an import receptor for L25-like proteins, Yrb4p localizes to the cytoplasm, the nucleoplasm and the NPC.

Random Mutagenesis and Functional Analysis of the Ran-binding Protein, RanBP1

“…The principal function of RanBP1 in nucleocytoplasmic transport is believed to be termination of the transport cycle and regeneration of free transport receptors in the cytosol (18,31,47,48). RanBP1 (and Nup358) performs this function by binding to Ran⅐GTP importin complexes and permitting access by RanGAP, which then hydrolyzes the GTP, thereby triggering dissociation of the Ran and the release of free importin.…”

Cselp functions as the nuclear export receptor for importin α in yeast

“…Characterized nuclear import and export receptors include, besides importin 13 (karyopherin [31) and its yeast homolog Kap95p [14][15][16][17][18], transportin (karyopherin [32) and yeast Kapl04p [19,20]), the import receptor for some hnRNP proteins, karyopherin [33 (yeast Pselp/Kapl21p) and [34 (yeast Yrb4p/Kap123p) [21][22][23], conferring nuclear import of ribosomal proteins, Mtrl0p [24,25], the nuclear import receptor for the yeast hnRNP protein Npl3p, Sxmlp [26], mediating nuclear import of the yeast La homolog, CRM1 (yeast Xpolp) [27][28][29][30], the export receptor for proteins containing a leucine-rich nuclear export signal (NES), and hLOS1 and yeast Loslp [31][32][33]), an export receptor for tRNA (for more references see [4,5]). …”

Potential molecular mechanisms for fruiting body formation of Cordyceps illustrated in the case ofCordyceps sinensis

“…G proteins can interact with adenylyl cyclases and catalyse the formation of cAMP (D’Souza and Heitman, 2001; Kamerewerd et al 2008). GTP-binding protein Ran belongs to the superfamily of Ras proteins and is crucial regulator of adenylyl cyclase (Schlenstedt et al 1997; Seewald et al 2003). Rab GDP-dissociation inhibitor (RabGDI) is a key regulator of Rab/Ypt GTPases that controls the distribution of active GTP and inactive GDP-bound forms between membranes and cytosol (Rak et al 2003).…”

“… Agaricus bisporus (De Groot et al 1997)19Spermidine synthaseC↑, E↑Development of spermidine synthase ( spsA ) null cells grown in the absence of spermidine produced fruiting bodies of Dictyostelium discoideum that have abnormally short stalks. Dictyostelium discoideum (Guo et al 1999)20Guanine nucleotide-binding protein (G protein) subunit beta-like proteinB↑, C↑↓G proteins are essential for growth, asexual and sexual development, and virulence in both animal and plant pathogenic filamentous species. In fungi, G proteins play integral roles for cell growth/division, mating, cell-cell fusion, morphogenesis, chemotaxis, virulence establishment, pathogenic development and secondary metabolite production. Aspergillus nidulans (Yu 2006; Li et al 2007)21GTP-binding nuclear protein Ran, putativeB↑GTP-binding protein Ran belongs to the superfamily of Ras proteins and is crucial regulator of adenylyl cyclase. Saccharomyces cerevisiae (Schlenstedt et al 1997; Seewald et al 2003)22Glyceraldehyde-3-phosphate dehydrogenaseD↓, E↑↓The glyceraldehyde-3-phosphate dehydrogenase gene GAPDH was expressed in both mycelia and fruiting bodies, suggesting that the GAPDH gene product is a heat shock protein which might be involved in the developmental phase of the Lentinus polychrous. Lentinus polychrous (Thanonkeo et al 2010)23Rab GDP-dissociation inhibitorA↑, C↓Rab GDP-dissociation inhibitor, a key regulator of Rab/Ypt GTPases that controls the distribution of the active GTP and inactive GDP-bound forms between membranes and cytosol, is up-regulated in fruiting body of mushroom Lentinula edodes.…”