The fission yeast Schizosaccharomyces pombe has two importin-alpha proteins, Imp1p and Cut15p, which have common and unique functions in nucleocytoplasmic transport and cell cycle progression.
The nuclear import of classical nuclear localization signal-containing proteins depends on importin-alpha transport receptors. In budding yeast there is a single importin-alpha gene and in higher eukaryotes there are multiple importin-alpha-like genes, but in fission yeast there are two: the previously characterized cut15 and the more recently identified imp1. Like other importin-alpha family members, Imp1p supports nuclear protein import in vitro. In contrast to cut15, imp1 is not essential for viability, but imp1delta mutant cells exhibit a telophase delay and mild temperature-sensitive lethality. Differences in the cellular functions that depend on Imp1p and Cut15p indicate that they each have unique physiological roles. They also have common roles because the imp1delta and the cut15-85 temperature-sensitive mutations are synthetically lethal; overexpression of cut15 partially suppresses the temperature sensitivity, but not the mitotic delay in imp1delta cells; and overexpression of imp1 partially suppresses the mitotic defect in cut15-85 cells but not the loss of viability. Both Imp1p and Cut15p are required for the efficient nuclear import of both an SV40 nuclear localization signal-containing reporter protein and the Pap1p component of the stress response MAP kinase pathway. Imp1p and Cut15p are essential for efficient nuclear protein import in S. pombe.
Umeda
Makoto
M
Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Izaddoost
Shahed
S
Cushman
Ian
I
Moore
Mary Shannon
MS
Sazer
Shelley
S
D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000595:Amino Acid Sequence; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism*; D015966:Gene Expression Regulation, Fungal; D005804:Genes, Lethal / Q000235:genetics; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D018384:Oxidative Stress; D010641:Phenotype; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012568:Schizosaccharomyces / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D028901:alpha Karyopherins / Q000235:genetics* / Q000378:metabolism
D050976:Basic-Leucine Zipper Transcription Factors; C510481:Cut15 protein, S pombe; C510480:Imp1 protein, S pombe; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; C105096:Pap1 protein, S pombe; D011993:Recombinant Fusion Proteins; D029702:Schizosaccharomyces pombe Proteins; D028901:alpha Karyopherins; D049452:Green Fluorescent Proteins