A RanBP1 mutation which does not visibly affect nuclear import may reveal additional functions of the ran GTPase system.
Ran, a nuclear GTPase, and a number of interacting proteins, including regulators RanGEF1 and RanGAP1, are involved in nucleocytoplasmic transport. We have identified a new temperature-sensitive mutation in budding yeast YRB1 gene, which encodes Ran-binding protein-1 (RanBP1). In contrast to other yrb1 alleles, the new mutation (yrb1-21) does not cause visible defects in import of nuclear proteins Npl3p, histone H2B, or beta-galactosidase fused to a nuclear localization signal. We hypothesize that the inviability of mutant cells at the restrictive temperature is caused by an additional essential function of RanBP1 other than nuclear import. This function may be revealed by the terminal phenotypes of yrb1-21, which include failure of the mitotic spindles to properly align along the mother-bud axis and accumulation of cells in late mitosis or G1 phase of the cell cycle. These features are shared, in part, by a mutation in RanGEF1, but not in RanGAP1. The yrb1-21 allele suppresses a RanGEF1 mutation, indicating that RanGEF1 and RanBP1 may be involved in the same essential function.
Department of Cell Biology, Baylor College of Medicine, Houston, Texas, 77030, USA. iliao@bcm.tmc.edu
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D001692:Biological Transport / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000235:genetics; D002467:Cell Nucleus / Q000201:enzymology / Q000235:genetics* / Q000648:ultrastructure; D018118:Chloride Channels; D004268:DNA-Binding Proteins / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics* / Q000502:physiology; D020558:GTP Phosphohydrolases / Q000235:genetics* / Q000502:physiology; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000502:physiology; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins / Q000235:genetics; D016296:Mutagenesis / Q000235:genetics*; D009687:Nuclear Proteins / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D011506:Proteins / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature; D020931:ran GTP-Binding Protein
D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D018118:Chloride Channels; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C089713:GEF1 protein, S cerevisiae; D020690:GTPase-Activating Proteins; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D009687:Nuclear Proteins; D011506:Proteins; D029701:Saccharomyces cerevisiae Proteins; C091775:ran-binding protein 1; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020931:ran GTP-Binding Protein