The identification of cDNAs that affect the mitosis-to-interphase transition in Schizosaccharomyces pombe, including sbp1, which encodes a spi1p-GTP-binding protein.
Perturbations of the spi1p GTPase system in fission yeast, caused by mutation or overexpression of several regulatory proteins, result in a unique terminal phenotype that includes condensed chromosomes, a wide medial septum, and a fragmented nuclear envelope. To identify potential regulators or targets of the spi1p GTPase system, a screen for cDNAs whose overexpression results in this terminal phenotype was conducted, and seven clones that represent three genes, named med1, med2, and med3 (mitotic exit defect), were identified. Their genetic interaction with the spi1p GTPase system was established by showing that the spi1p guanine nucleotide exchange factor mutant pim1-d1ts was hypersensitive to their overexpression. med1 encodes a homologue of the human Ran-binding protein, RanBP1, and has been renamed sbp1 (spi1-binding protein). sbp1p binds to spi1p-GTP and costimulates the GTPase-activating protein (GAP)-catalyzed GTPase activity. Cells in which sbp1p is depleted or overproduced phenocopy cells in which the balance between spi1p-GTP and spi1p-GDP is perturbed by other means. Therefore, sbp1p mediates and/or regulates the essential functions of the spi1p GTPase system. med2 and med3 encode novel fission yeast proteins that, based on our phenotypic analyses, are likely to identify additional regulators or effectors of the spi1p GTPase system.
He
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Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, Texas 77030, USA.
Hayashi
N
N
Walcott
N G
NG
Azuma
Y
Y
Patterson
T E
TE
Bischoff
F R
FR
Nishimoto
T
T
Sazer
S
S
D000595:Amino Acid Sequence; D001483:Base Sequence; D002453:Cell Cycle / Q000502:physiology; D002470:Cell Survival / Q000235:genetics; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics; D018076:DNA, Complementary / Q000737:chemistry; D019143:Evolution, Molecular; D005434:Flow Cytometry; D005656:Fungal Proteins / Q000737:chemistry*; D020558:GTP Phosphohydrolases / Q000235:genetics; D019204:GTP-Binding Proteins / Q000737:chemistry*; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D008938:Mitosis / Q000235:genetics*; D008969:Molecular Sequence Data; D020559:Monomeric GTP-Binding Proteins; D009687:Nuclear Proteins / Q000737:chemistry; D012568:Schizosaccharomyces / Q000737:chemistry*; D029702:Schizosaccharomyces pombe Proteins; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D020931:ran GTP-Binding Protein
D018076:DNA, Complementary; D005656:Fungal Proteins; D009687:Nuclear Proteins; C111826:Sbp1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; C091775:ran-binding protein 1; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D020559:Monomeric GTP-Binding Proteins; D020931:ran GTP-Binding Protein