Fluphenazine-resistant Saccharomyces cerevisiae mutants defective in the cell division cycle

Genetic characterization of genes encoding enzymes catalyzing addition of phospho-ethanolamine to the glycosylphosphatidylinositol anchor in Saccharomyces cerevisiae

MPC1/GPI13/YLL031C, one of the genes involved in the addition of phospho-ethanolamine to the glycosylphosphatidylinositol (GPI) anchor core, is an essential gene. Three available temperature-sensitive mutant alleles, mpc1-3, mpc1-4, and mpc1-5, displayed different phenotypes to each other and, correspondingly, these mutants were found to have different mutations in the MPC1 ORF. Temperature-sensitivity of mpc1-5 mutants was suppressed by 5 mM ZnSO(4) and by 5 mM MnCl(2). Multicopy suppressors were isolated from mpc1-5 mutant. Suppressors commonly effective to mpc1-4 and mpc1-5 mutations are PSD1, encoding phosphatidylserine decarboxylase, and ECM33, which were found to suppress the temperature-sensitive phenotype shown by the fsr2-1 and las21delta mutants, those of which have defects in the GPI anchor synthesis. PSD2, encoding another phosphatidylserine decarboxylase that is localized in Golgi/vacuole, was found to be able to serve as a multicopy suppressor of mpc1 and fsr2-1 mutants but not of the las21 delta mutant. In contrast to psd1delta, psd2delta showed a synthetic growth defect with mpc1 mutants but not with fsr2-1 or las21delta. Furthermore, psd1delta psd2delta mpc1 triple mutants did not form colonies on nutrient medium unless ethanolamine was supplied to the medium, whereas psd1delta psd2 delta fsr2-1 or psd1delta psd2 delta las21delta triple mutants grew on nutrient medium without supplementation of ethanolamine. These observations suggest that Mpc1 preferentially utilizes phosphatidylethanolamine produced by Psd2 that is localized in Golgi/vacuole. fsr2-1 dpl1 Delta psd1delta strains showed slower growth than fsr2-1 dpl1delta psd2 delta, suggesting that Fsr2 enzyme depends more on Dpl1 and Psd1 for production of phosphatidylethanolamine. Las21 did not show preference for the metabolic pathway to produce phosphatidylethanolamine.

Defects in glycosylphosphatidylinositol (GPI) anchor synthesis activate Hog1 kinase and confer copper-resistance in Saccharomyces cerevisisae

Las21/Gpi7 contains a heavy-metal-associated motif at its N-terminus. When this motif was disrupted by amino acid substitution, the cells acquired weak copper-resistance. We found that the previously isolated las21 mutants were strongly resistant to copper. Metallothionein is necessary for the expression of the copper-resistance of the las21 mutants. However, hyper-production of metallothionein is unlikely to be the cause of copper-resistance of the las21 mutants. Copper-sensitive mutants (collectively called Cus mutants) were isolated from the las21delta and characterized. One of the Cus genes was found to be PBS2, which encodes Hog1 MAP kinase kinase, indicating that the Hog1 MAP kinase pathway is needed for the expression of copper-resistance of the las21 mutants. As expected, the las21delta hog1delta strain was no longer copper-resistant. We found that Hog1 was constitutively activated in las21delta cells and in ssk1delta las21delta cells but not in sho1delta las21delta cells. Inactivation of either FSR2/MCD4 or MPC1/GPI13, both of which are involved in GPI anchor synthesis, like LAS21, caused a similar level of constitutive activation of Hog1 kinase and copper-resistance as found in the las21delta strain. The constitutive activation was canceled by introducing the sskl mutation, but not the sho1 mutation, in each GPI anchor mutant tested, suggesting that the defect in GPI anchor synthesis specifically affects the Slnl branch of the MAP kinase pathway. Since the wild-type cells grown in YPD containing 0.5 M NaCl do not show copper-resistance, mere activation of Hog1 is not sufficient for expression of copper-resistance. We propose that a defect in GPI anchor synthesis has multiple consequences, including activation of the Hog1 MAP kinase cascade and conferring copper-resistance.

Three yeast genes, PIR1, PIR2 and PIR3, containing internal tandem repeats, are related to each other, and PIR1 and PIR2 are required for tolerance to heat shock

We isolated three highly homologous genes, PIR1, PIR2 and PIR3, collectively called the PIR genes. The remarkable feature of their putative amino acid sequence is that they contain a sequence consisting of 18-19 amino acid residues repeated tandemly seven to ten times. Genes homologous to PIR were found in Kluyveromyces lactis and Zygosaccharomyces rouxii but not in Schizosaccharomyces pombe, suggesting that a set of PIR genes plays some role in budding yeast. Bias of codon usage seen in each of the PIR translation products suggests that they are expressed abundantly. The fact that disruption of each gene is viable indicates that none of them is essential. The double disruptants, pir1 pir2, were viable under various conditions, such as higher temperature (37 degrees C) or high salt concentration, but showed a slow-growing phenotype on an agar slab. Furthermore, they were sensitive to heat shock. Addition of a pir3 disruption to the pir1 pir2 double disruptant brought about no phenotypic difference from the original double mutant. PIR1 and PIR3 are closely linked to each other and are on chromosome XI.

The complete sequence of a 19,482 bp segment located on the right arm of chromosome II from Saccharomyces cerevisiae

We report here the sequence of a 19,482 bp DNA segment of chromosome II of Saccharomyces cerevisiae. The fragment contains 16 open reading frames (ORFs) covering 74% of the sequence. Four predicted products present homology with known proteins. The ORF YBR1732 exhibits a strong homology to serine hydroxymethyl transferase; the best score is 53.1% identity in 458 amino acids overlap with the serine hydroxymethyl transferase from rabbit liver. YBR1724, which shows homology with riboflavin synthase of Bacillus subtilis, is probably the RIB5 gene implied in riboflavine synthesis and mapped in this region. YBR1733 is homologous to rab protein and YBR1728 is presumably a GTPase activating protein.

Isolation and characterization of mutants supersensitive to the spindle poison, isopropyl N-3-chlorophenyl carbamate (CIPC) in the fission yeast Schizosaccharomyces pombe

Mutants supersensitive to the spindle poison, Isopropyl N-3-chlorophenyl carbamate (CIPC) of the fission yeast Schizosaccharomyces pombe were isolated and characterized genetically. Fourteen different recessive loci were assigned for the mutation (donated as cps1 to cps14) and two, cps1 and cps3, were mapped precisely on the chromosomes. Nine mutant strains were also supersensitive to phenothiazine derivatives, inhibitors of calcium-binding protein calmodulin. Four of nine strains were incapable of growing in the presence of 10 microM calcium ionophore A23187, at which the drug had no effect on cell growth in other strains. Fluorescence microscopy using the DAPI and Calcofluor staining methods showed two strains out of four to be defective in normal cell division; most stationary-phase cells of the cps6 mutant were seen to be bi- or tetra-nucleate, being partitioned with one or three septa, respectively. In the other mutant (cps8), enlarged cells were unequally partitioned with multisepta, and each compartment contained several daughter nuclei. The septa appeared aberrant in position within the cell, and situated diagonally but not vertically along the long cell axis.

Characterization of a staurosporine- and temperature-sensitive mutant, stt1, of Saccharomyces cerevisiae: STT1 is allelic to PKC1

Staurosporine is an antibiotic that specifically inhibits protein kinase C. Fourteen staurosporine- and temperature-sensitive (stt) mutants of Saccharomyces cerevisiae were isolated and characterized. These mutants were divided into ten complementation groups, and characterized for their cross-sensitivity to K-252a, neomycin, or CaCl2. The STT1 gene was cloned and sequenced. The nucleotide sequence of the STT1 gene revealed that STT1 is the same gene as PKC1. The STT1 gene conferred resistance to staurosporine on wild-type cells, when present on a high copy number plasmid. STT1/stt1::HIS3 diploid cells were more sensitive to staurosporine than STT1/STT1 diploid cells. Analysis of temperature-sensitive stt1 mutants showed that the STT1 gene product functioned in S or G2/M phase. These results suggest that a protein kinase (the STT1 gene product) is one of the essential targets of staurosporine in yeast cells.

Vertebrate and yeast calmodulin, despite significant sequence divergence, are functionally interchangeable

Yeast strains relying solely on vertebrate (Xenopus laevis) calmodulin, expressed under control of a yeast (GAL1) promoter, grew at the same rate as yeast cells containing their endogenous calmodulin. Therefore, the ability to perform essential functions has been conserved between yeast and vertebrate calmodulins, suggesting that calmodulin performs the same (or overlapping) roles in yeast as it does in higher eukaryotes. Successful substitution of vertebrate for yeast calmodulin also suggests that the two proteins can adopt similar conformations in vivo, despite the large number of amino acid differences between them (60 out of 148 residues). Strains overproducing either vertebrate or yeast calmodulin about 100-fold and a strain producing a normal level of yeast calmodulin were essentially indistinguishable in many characteristics, including microtubule distribution, rate of secretion, response to mating pheromone, sporulation, and adaptation to nutrient limitation. Calmodulin overproduction did not confer elevated resistance to a phenothiazine drug, trifluoperazine, thought to be a calmodulin-specific inhibitor. These results have important implications for understanding the role of calmodulin in intracellular calcium signaling.