scholarly journals Fission Yeast Ras1 Effector Scd1 Interacts With the Spindle and Affects Its Proper Formation

Genetics ◽  
2000 ◽  
Vol 156 (3) ◽  
pp. 995-1004
Author(s):  
Ying-chun Li ◽  
Chang-rung Chen ◽  
Eric C Chang
Keyword(s):  
Chromosome Segregation ◽  
Spindle Pole ◽  
Nucleotide Exchange ◽  
Spindle Formation ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Spindle Pole Bodies ◽  
Synthetically Lethal ◽  
Tubulin Mutations ◽  
Localization Data

Abstract Ras1 GTPase is the Schizosaccharomyces pombe homolog of the mammalian Ha-Ras proto-oncoprotein. Ras1 interacts with Scd1 (aka Ral1), a presumptive guanine nucleotide exchange factor for Cdc42sp, to control organization of the cytoskeleton. In this study, we demonstrated that the scd1 deletion (scd1Δ) induced hypersensitivity to microtubule destabilizing drugs and instability of the minichromosome. Overexpression of scd1 induced formation of abnormal spindles and chromosome missegregation. The scd1 deletion worsened the defects of spindle formation in tubulin mutants; by contrast, it did not induce lethality in mutants defective in the spindle pole bodies. These genetic data suggest that Scd1 can interact with tubulin with substantial specificity to affect proper spindle formation and chromosome segregation. Subcellular localization data further illustrated that a GFP-Scd1 fusion protein can associate with the spindle. Finally, we showed that unlike ras1Δ and scd1Δ, byr2Δ (affecting the Ras1 effector for mating) is not synthetically lethal with the tubulin mutations. These data collectively suggest that the Ras1 pathway can impinge upon microtubules through Scd1, but not Byr2, to affect proper spindle formation and chromosome segregation.

scholarly journals Checkpoint control of mitotic exit—do budding yeast mind the GAP?

2006 ◽  
Vol 172 (3) ◽  
pp. 331-333 ◽  
Author(s):  
John A. Cooper ◽  
Scott A. Nelson
Keyword(s):  
Budding Yeast ◽  
Spindle Pole ◽  
Small Gtpase ◽  
Mitotic Exit ◽  
Cell Cycle Checkpoints ◽  
Nucleotide Exchange ◽  
Checkpoint Control ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Spindle Pole Bodies

Cell cycle checkpoints can delay mitotic exit in budding yeast. The master controller is the small GTPase Tem1, with inputs from a proposed guanine nucleotide exchange factor (GEF), Lte1, and a GTPase-activating protein (GAP), Bub2/Bfa1. In this issue, Fraschini et al. (p. 335) show that GAP activity of Bub2/Bfa1 appears to be dispensable for inactivation of Tem1 in cells. Their results call into question the GTP/GDP switch model for Tem1 activity, as have other results in the past. The paper also focuses attention on the two spindle pole bodies as potential sites for regulation of Tem1.

scholarly journals Lte1 contributes to Bfa1 localization rather than stimulating nucleotide exchange by Tem1

2009 ◽  
Vol 187 (4) ◽  
pp. 497-511 ◽  
Author(s):  
Marco Geymonat ◽  
Adonis Spanos ◽  
Geoffroy de Bettignies ◽  
Steven G. Sedgwick
Keyword(s):  
Mutational Analysis ◽  
Spindle Pole ◽  
Cell Polarization ◽  
Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Spindle Pole Bodies ◽  
Guanosine Triphosphatase ◽  
Spindle Position ◽  
Mitotic Regulation

Lte1 is a mitotic regulator long envisaged as a guanosine nucleotide exchange factor (GEF) for Tem1, the small guanosine triphosphatase governing activity of the Saccharomyces cerevisiae mitotic exit network. We demonstrate that this model requires reevaluation. No GEF activity was detectable in vitro, and mutational analysis of Lte1’s putative GEF domain indicated that Lte1 activity relies on interaction with Ras for localization at the bud cortex rather than providing nucleotide exchange. Instead, we found that Lte1 can determine the subcellular localization of Bfa1 at spindle pole bodies (SPBs). Under conditions in which Lte1 is essential, Lte1 promoted the loss of Bfa1 from the maternal SPB. Moreover, in cells with a misaligned spindle, mislocalization of Lte1 in the mother cell promoted loss of Bfa1 from one SPB and allowed bypass of the spindle position checkpoint. We observed that lte1 mutants display aberrant localization of the polarity cap, which is the organizer of the actin cytoskeleton. We propose that Lte1’s role in cell polarization underlies its contribution to mitotic regulation.

scholarly journals The Fission Yeast spo14 + Gene Encoding a Functional Homologue of Budding Yeast Sec12 Is Required for the Development of Forespore Membranes

2003 ◽  
Vol 14 (3) ◽  
pp. 1109-1124 ◽  
Author(s):  
Michiko Nakamura-Kubo ◽  
Taro Nakamura ◽  
Aiko Hirata ◽  
Chikashi Shimoda
Keyword(s):  
Secretory Pathway ◽  
Protein Transport ◽  
Membrane Vesicles ◽  
Spindle Pole ◽  
Nucleotide Exchange ◽  
Gene Encoding ◽  
Single Nucleotide Change ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Cold Sensitive

The Schizosaccharomyces pombe spo14-B221 mutant was originally isolated as a sporulation-deficient mutant. However, thespo14 + gene is essential for cell viability and growth. spo14 + is identical to the previously characterizedstl1 + gene encoding a putative homologue of Saccharomyces cerevisiae Sec12, which is essential for protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus. In the spo14 mutant cells, ER-like membranes were accumulated beneath the plasma membrane and the ER/Golgi shuttling protein Rer1 remained in the ER. Sec12 is a guanine nucleotide exchange factor for the Sar1 GTPase. Overproduction ofpsr1 + coding for an S. pombe Sar1 homologue suppressed both the sporulation defect ofspo14-B221 and cold-sensitive growth of newly isolatedspo14-6 and spo14-7 mutants. These results indicate that Spo14 is involved in early steps of the protein secretory pathway. The spo14-B221 allele carries a single nucleotide change in the branch point consensus of the fifth intron, which reduces the abundance of the spo14 mRNA. During meiosis II, the forespore membrane was initiated near spindle pole bodies; however, subsequent extension of the membrane was arrested before its closure into a sac. We conclude that Spo14 is responsible for the assembly of the forespore membrane by supplying membrane vesicles.

scholarly journals Two Ras Pathways in Fission Yeast Are Differentially Regulated by Two Ras Guanine Nucleotide Exchange Factors

2002 ◽  
Vol 22 (13) ◽  
pp. 4598-4606 ◽  
Author(s):  
Piyi Papadaki ◽  
Véronique Pizon ◽  
Brian Onken ◽  
Eric C. Chang
Keyword(s):  
Mitogen Activated Protein Kinase ◽  
Critical Element ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Signaling Specificity ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factor ◽  
Mitogen Activated Protein ◽  
Kinase Cascade ◽  
Synthetically Lethal

ABSTRACT How a given Ras prreotein coordinates multiple signaling inputs and outputs is a fundamental issue of signaling specificity. Schizosaccharomyces pombe contains one Ras, Ras1, that has two distinct outputs. Ras1 activates Scd1, a presumptive guanine nucleotide exchange factor (GEF) for Cdc42, to control morphogenesis and chromosome segregation, and Byr2, a component of a mitogen-activated protein kinase cascade, to control mating. So far there is only one established Ras1 GEF, Ste6. Paradoxically, ste6 null (ste6Δ) mutants are sterile but normal in cell morphology. This suggests that Ste6 specifically activates the Ras1-Byr2 pathway and that there is another GEF capable of activating the Scd1 pathway. We thereby characterized a potential GEF, Efc25. Genetic data place Efc25 upstream of the Ras1-Scd1, but not the Ras1-Byr2, pathway. Like ras1Δ and scd1Δ, efc25Δ is synthetically lethal with a deletion in tea1, a critical element for cell polarity control. Using truncated proteins, we showed that the C-terminal GEF domain of Efc25 is essential for function and regulated by the N terminus. We conclude that Efc25 acts as a Ras1 GEF specific for the Scd1 pathway. While ste6 expression is induced during mating, efc25 expression is constitutive. Moreover, Efc25 overexpression renders cells hyperelongated and sterile; the latter can be rescued by activated Ras1. This suggests that Efc25 can recruit Ras1 to selectively activate Scd1 at the expense of Byr2. Reciprocally, Ste6 overexpression can block Scd1 activation. We propose that external signals can partly segregate two Ras1 pathways by modulating GEF expression and that GEFs can influence how Ras is coupled to specific effectors.

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