A halotolerant mutant of Saccharomyces cerevisiae.

FRD, a nuclear and dominant spontaneous mutant of Saccharomyces cerevisiae capable of growing in up to 2 M NaCl, was isolated. Compared with parental cells, the mutant cells have a lower intracellular Na+/K+ ratio, shorter generation times in the presence of 1 M NaCl, and alterations in gene expression.     

啤酒酵母DNA修复基因RAD24温度敏感突变株的分离及其特性的初步研究

以ＹＣｐｌａｃ系列带Ｔｒｐ、Ｈｉｓ和Ｕｒａ标志基因的载体为骨架构建含野生型和经羟胺处理的突变型的啤酒酵母ＲＡＤ２４基因质粒,用质粒替换方法分离ＲＡＤ２４基因温度敏感突变株（ｒａｄ２４－ｔｓ３）．紫外生存试验发现,ｒａｄ２４－ｔｓ３对紫外线敏感;同位素（３Ｈ－ＴｄＲ,３Ｈ－ＵＲ,３Ｈ－Ｌｅｕ）参入试验表明,该突变株ＤＮＡ、ＲＮＡ及蛋白质合成均较野生型明显降低．     

Effect of aPMR1 disruption on the processing of heterologous glycoproteins secreted in the yeastSaccharomyces cerevisiae

TheSaccharomyces cerevisiae PMR1 gene encodes a Ca²⁺-ATPase localized in the Golgi. We have investigated the effects ofPMR1 disruption inS. cerevisiae on the glycosylation and secretion of three heterologous glycoproteins, human α₁-antitrypsin (α₁-AT), human antithrombin III (ATHIII), andAspergillus niger glucose oxidase (GOD). Thepmr1 null mutant strain secreted larger amounts of ATHIII and GOD proteins per a unit cell mass than the wild type strain. Despite a lower growth rate of thepmr1 mutant, two-fold higher level of human ATHIII was detected in the culture supernatant from thepmr1 mutant compared to that of the wild-type strain. Thepmr1 mutant strain secreted α₁-AT and the GOD proteins mostly as core-glycosylated forms, in contrast to the hyperglycosylated proteins secreted in the wild-type strain. Furthermore, the core-glycosylated forms secreted in thepmr1 mutant migrated slightly faster on SDS-PAGE than those secreted in themnn9 deletion mutant and the wild type strains. Analysis of the recombinant GOD with anti-α1,3-mannose antibody revealed that GOD secreted in thepmr1 mutant did not have terminal α1,3-linked mannoses unlike those secreted in themnn9 mutant and the wild type strains. The present results indicate that thepmr1 mutant, with the super-secretion phenotype, is useful as a host system to produce recombinant glycoproteins lacking high-mannose outer chains.     

Optimal conditions for the analysis of Pasteurella haemolytica lipopolysaccharide by sodium dodecyl sulphate-polyacrylamide gel electrophoresis

Monomeric human calcitonin (hCT) gene and oligomeric hCT genes composed of two, three or four head-to-tail linked monomers were fused in-frame to the yeast alpha-factor leader coding sequence wild-type and fragile mutant Saccharomyces cerevisiae strains were transformed with the constructed plasmids and the yield of recombinant protein secreted into the culture medium was measured. The yeast cells secreted equal (molar) amounts of all of the hCT variants. The recombinant proteins remained stable in the growth medium for at least 3 days. The fragile cells secreted about 30% more hCT as compared to the wild-type yeast cells.     

The proteinase yscB inhibitor (PB12) gene of yeast and studies on the function of its protein product

The gene for proteinase yscB inhibitor I2B (PBI2) from Saccharomyces cerevisiae was isolated by oligonucleotide screening of a genomic DNA library, and was sequenced. The gene codes for a single protein of 75 amino acids. In contrast to the published amino acid sequence [Maier, K., Müller, H., Tesch, R., Trolp, T., Witt, I. & Holzer, H. (1979) J. Biol. Chem. 254, 12,555-12,561] the DNA sequence revealed a valine instead of a leucine at position 33 (32 of the mature protein). Therefore the primary sequences of the isoinhibitors I2B of S. cerevisiae and I1B of Saccharomyces carlsbergensis differ only at position 34 (glutamic acid/lysine). The open reading frame of PBI2 was replaced in vitro by the URA3 gene and a I2B null mutant of S. cerevisiae was constructed by gene replacement. The mutation resulted in an elevation of the protein degradation rate by 50% when grown under nutritional stress compared to the isogenic wild type. Growth and viability of the cells was not significantly affected by the absence of I2B.     

SAM1, the structural gene for one of the S-adenosylmethionine synthetases in Saccharomyces cerevisiae. Sequence and expression

Saccharomyces cerevisiae contains two genes, SAM1 and SAM2, encoding functional S-adenosylmethionine synthetases. The gene SAM1 was isolated by functional complementation of a double mutant of S. cerevisiae, and its identity was confirmed by gene disruption. The cloned gene was used to probe wild type chromosomal DNA, and two regions hybridizing with SAM1 were found, one of which is the SAM1 region. The DNA sequence of SAM1 is reported. The translation product shows a high homology with the one deduced from the sequence of the MetK gene encoding the SAM synthetase of Escherichia coli.     

Yeast resistance to polyene antibiotics. VI. Isolation and biochemical analysis of strains of Saccharomyces cerevisiae yeasts with mutations in the 2 nystatin-resistance genes

The comparative analysis of sterol content in the yeast Saccharomyces cerevisiae strains singly or doubly defective in nystatin resistance genes was carried out. The strains with two mutations in NYS genes were shown to accumulate the sterol mixture, similar to that of the parental singly defective mutant. This type of gene interaction allows to define the main biochemical order of reaction in ergosterol synthesis: methylation in C24 (NYS1), delta 8----delta 7 isomerization (NYS2), C5 (6) and C22 (23) desaturation (NYS3 and NYSX).     

N-Glycosylation of secretion enhancer peptide as influencing factor for the secretion of target proteins from Saccharomyces cerevisiae

hIL-1beta-derived polypeptide, when fused to the N-terminal end of target proteins, exerts a potent secretion enhancer function in Saccharomyces cerevisiae. We investigated the effect of N-glycosylation of the secretion enhancer peptide on the secretion of target proteins. The N-terminal 24 amino acids (Ser5-Ala28) of human interleukin 1beta (hIL-1beta) and interleukin 1 receptor antagonist (IL-1ra) were used as secretion enhancer for synthesizing recombinant human granulocyte-colony stimulating factor (rhG-CSF) from S. cerevisiae. The mutation of potential N-glycosylation site, by substituting Gln for either Asn7 of N-terminal 24 amino acids of hIL-1beta (Asn7Gln) or Asn84 of IL-1ra (Asn84Gln), resulted in a dramatic reduction of rhG-CSF secretion efficiency. In contrast, the mutant containing an additional N-glycosylation site on the N-terminal 24 amino acids of hIL-1beta (Gln15Asn) secreted twice as much rhG-CSF into culture media as wild type hIL-1beta. These results show that N-glycosylation of the secretion enhancer peptide plays an important role in increasing the secretion efficiency of the downstream target proteins. The results also suggest that judicious choice of enhancer peptide and the control of its glycosylation could be of general utility for secretory production of heterologous proteins from S. cerevisiae.     

The gene encoding the phosphatidylinositol transfer protein is essential for cell growth

Phosphatidylinositol transfer proteins (PI-TPs) catalyze the transfer of phosphatidylinositol and phosphatidylcholine between membranes in vitro. However, the in vivo function of these proteins is unknown. In this paper, we use a combined biochemical and genetic approach to determine the importance of PI-TP in vivo. An oligonucleotide based on the amino-terminal sequence of the PI-TP from Saccharomyces cerevisiae was used to screen a yeast genomic library for the gene encoding PI-TP (PIT1 gene). Positive clones showed overproduction of transfer activities and transfer protein in the 100,000 x g supernatants. The 5' terminus of the PIT1 gene correlates with the predicted codons for residues 3-30 of the determined protein sequence. A putative intron is located between the codons for residues 2 and 3 of the protein sequence. The codons for the first two amino acids of the protein and the presumptive initiation methionine precede the intron. Tetrad analysis of a heterozygous diploid (PIT1/pit1::LEU2) revealed that the PIT1 gene is essential for cell growth. Nonviable spores could be rescued by transformation of the above diploid prior to sporulation, with a plasmid-borne copy of the wild type gene.     

The inheritance of mtDNA in lager brewing strains

In this work, we compared the mtDNA of a number of interspecific Saccharomyces hybrids (Saccharomyces cerevisiae x Saccharomyces uvarum and S. cerevisiae x Saccharomyces bayanus) to the mtDNA of 22 lager brewing strains that are thought to be the result of a natural hybridization between S. cerevisiae and another Saccharomyces yeast, possibly belonging to the species S. bayanus. We detected that in hybrids constructed in vitro, the mtDNA could be inherited from either parental strain. Conversely, in the lager strains tested, the mtDNA was never of the S. cerevisiae type. Moreover, the nucleotide sequence of lager brewing strains COXII gene was identical to S. bayanus strain NBRC 1948 COXII gene. MtDNA restriction analysis carried out with three enzymes confirmed this finding. However, restriction analysis with a fourth enzyme (AvaI) provided restriction patterns for lager strains that differed from those of S. bayanus strain NBRC 1948. Our results raise the hypothesis that the human-driven selection carried out on existing lager yeasts has favored only those bearing optimal fermentation characteristics at low temperatures, which harbor the mtDNA of S. bayanus.     

CHS5, a gene involved in chitin synthesis and mating in Saccharomyces cerevisiae.

The CHS5 locus of Saccharomyces cerevisiae is important for wild-type levels of chitin synthase III activity. chs5 cells have reduced levels of this activity. To further understand the role of CHS5 in yeast, the CHS5 gene was cloned by complementation of the Calcofluor resistance phenotype of a chs5 mutant. Transformation of the mutant with a plasmid carrying CHS5 restored Calcofluor sensitivity, wild-type cell wall chitin levels, and chitin synthase III activity levels. DNA sequence analysis reveals that CHS5 encodes a unique polypeptide of 671 amino acids with a molecular mass of 73,642 Da. The predicted sequence shows a heptapeptide repeated 10 times, a carboxy-terminal lysine-rich tail, and some similarity to neurofilament proteins. The effects of deletion of CHS5 indicate that it is not essential for yeast cell growth; however, it is important for mating. Deletion of CHS3, the presumptive structural gene for chitin synthase III activity, results in a modest decrease in mating efficiency, whereas chs5delta cells exhibit a much stronger mating defect. However, chs5 cells produce more chitin than chs3 mutants, indicating that CHS5 plays a role in other processes besides chitin synthesis. Analysis of mating mixtures of chs5 cells reveals that cells agglutinate and make contact but fail to undergo cell fusion. The chs5 mating defect can be partially rescued by FUS1 and/or FUS2, two genes which have been implicated previously in cell fusion, but not by FUS3. In addition, mating efficiency is much lower in fus1 fus2 x chs5 than in fus1 fus2 x wild type crosses. Our results indicate that Chs5p plays an important role in the cell fusion step of mating.     

The Saccharomyces cerevisiae gene SDS22 encodes a potential regulator of the mitotic function of yeast type 1 protein phosphatase.

In higher eukaryotes, the activity and specificity of the type 1 protein serine-threonine phosphatase (PP1) catalytic subunit is thought to be controlled by its association with a number of regulatory or targeting subunits. Here we describe the characterization of a gene encoding one such potential polypeptide in the yeast Saccharomyces cerevisiae. The gene which we have isolated (termed SDS22) encodes a product with a high degree of sequence identity to the fission yeast sds22 protein, a known regulator of the mitotic function of PP1 in Schizosaccharomyces pombe. Using two different criteria, we have demonstrated that Sds22p and the catalytic subunit of PP1 (Glc7p) interact in yeast cells. We have also generated a temperature-sensitive allele of GLC7 (glc7-12) which causes a block to the completion of mitosis at the restrictive temperature. Additional copies of SDS22 lead to allele-specific suppression of the glc7-12 mutant, strongly suggesting that the interaction between the two proteins is of functional significance. Sds22p is therefore likely to be the second example of a PP1 regulatory subunit identified in S. cerevisiae.     

The Saccharomyces cerevisiae CWH8 gene is required for full levels of dolichol-linked oligosaccharides in the endoplasmic reticulum and for efficient N-glycosylation

The Saccharomyces cerevisiae mutant cwh8 was previously found to have an anomalous cell wall. Here we show that the cwh8 mutant has an N -glycosylation defect. We found that cwh8 cells were resistant to vanadate and sensitive to hygromycin B, and produced glycoforms of invertase and carboxypeptidase Y with a reduced number of N -chains. We have cloned the CWH8 gene. We found that it was nonessential and encoded a putative transmembrane protein of 239 amino acids. Comparison of the in vitro oligosaccharyl transferase activities of membrane preparations from wild type or cwh8 Delta cells revealed no differences in enzyme kinetic properties indicating that the oligosaccharyl transferase complex of mutant cells was not affected. cwh8 Delta cells also produced normal dolichols and dolichol-linked oligosaccharide intermediates including the full-length form Glc3Man9GlcNAc2. The level of dolichol-linked oligosaccharides in cwh8 Delta cells was, however, reduced to about 20% of the wild type. We propose that inefficient N -glycosylation of secretory proteins in cwh8 Delta cells is caused by an insufficient supply of dolichol-linked oligosaccharide substrate.     

Isolation and characterization of OLE1, a gene affecting fatty acid desaturation from Saccharomyces cerevisiae

The unsaturated fatty acid (ufa) requiring ole1 mutant of Saccharomyces cerevisiae appears to produce a defective delta-9 fatty acid desaturase. This enzyme catalyzes double bond formation between carbons 9 and 10 of palmitoyl and stearoyl coenzyme A. A DNA fragment isolated by complementation of an ole1 strain repairs the ufa requirement in mutant cells. Genetic analysis of the cloned DNA fragment indicates that it is allelic to the OLE1 gene. Disruption of a single copy of the wild type gene in a diploid strain produces both wild type and nonreverting ufa-requiring haploid progeny upon sporulation. Membrane lipids of the disrupted haploid strains contain only ufas supplied in the growth medium. The recovery of activity in both wild type and disrupted segregants was examined after removal of ufas from the growth medium. Following ufa deprivation disruptant cells grew normally for about three generations and then at a slower rate for at least 0.6 generations. During that time cellular ufas dropped from 63 to 7.3 mol % of the total fatty acids. No production of the 16:1 and 18:1 products of the desaturase was observed in disruptant cells, whereas desaturation in wild type control cells was evident 2 h after deprivation. These results indicate that 1) the OLE1 gene is essential for production of monounsaturated fatty acids and is probably the structural gene for the delta-9 desaturase enzyme. 2) A large part of membrane ufas present under normal culture conditions are not essential for growth and cell division.     

Identification of the genes affecting the regulation of riboflavin synthesis in the flavinogenic yeast Pichia guilliermondii using insertion mutagenesis

Pichia guilliermondii is a representative of a group of so-called flavinogenic yeast species that overproduce riboflavin (vitamin B(2)) in response to iron limitation. Using insertion mutagenesis, we isolated P. guilliermondii mutants overproducing riboflavin. Analysis of nucleotide sequence of recombination sites revealed that insertion cassettes integrated into the genome disrupting P. guilliermondii genes similar to the VMA1 gene of Ashbya gossypii and Saccharomyces cerevisiae and FES1 and FRA1 genes of S. cerevisiae. The constructed P. guilliermondiiΔvma1-17 mutant possessed five- to sevenfold elevated riboflavin production and twofold decreased iron cell content as compared with the parental strain. Pichia guilliermondiiΔfra1-45 mutant accumulated 1.8-2.2-fold more iron in the cells and produced five- to sevenfold more riboflavin as compared with the parental strain. Both Δvma1-17 and Δfes1-77 knockout strains could not grow at 37 °C in contrast to the wild-type strain and the Δfra1-45 mutant. Increased riboflavin production by the wild-type strain was observed at 37 °C. Although the Δfes1-77 mutant did not overproduce riboflavin, it showed partial complementation when crossed with previously isolated P. guilliermondii riboflavin-overproducing mutant rib80-22. Complementation analysis revealed that Δvma1-17 and Δfra1-45 mutants are distinct from previously reported riboflavin-producing mutants hit1-1, rib80-22 and rib81-31 of this yeast.     

Mutations of the alpha-galactosidase signal peptide which greatly enhance secretion of heterologous proteins by yeast.

The Saccharomyces carlsbergensis MEL1 gene encodes alpha-galactosidase (melibiase; MEL1) which is readily secreted by yeast cells into the culture medium. To evaluate the utility of the MEL1 signal peptide (sp) for the secretion of heterologous proteins by Saccharomyces cerevisiae, an expression vector was constructed which contains the MEL1 promoter and MEL1 sp coding sequence (MEL1sp). The coding sequences for echistatin (Echis) and human plasminogen activator inhibitor type 1 (PAI-1) were inserted in-frame with the MEL1sp. S. cerevisiae transformants containing the resulting expression vectors secreted negligible amounts of either Echis or PAI-1. Using site-directed mutagenesis, several mutations were introduced into the MEL1sp. Two mutations were identified which dramatically increased the secretion of both Echis and PAI-1 to levels similar to those achieved when using the yeast MF alpha 1 pre-pro secretory leader. In particular, increasing the hydrophobicity of the core region plus the addition of a positive charge to the N-terminal domain of the MEL1 sp resulted in the greatest increase in the secretion levels of those two proteins.     

The prepro-peptide of Mucor rennin directs the secretion of human growth hormone by Saccharomyces cerevisiae

An aspartic proteinase, Mucor pusillus rennin (MPR), of filamentous fungus Mucor pusillus, is efficiently secreted from a transformant of Saccharomyces cerevisiae containing the intact MPR gene. To test the usefulness of the MPR leader peptide in secretion of heterologous proteins from yeast cells, several plasmids encoding the fusion proteins composed of different parts of the NH2-terminal region of prepro-MPR and human growth hormone (hGH) were constructed. The parts of the leader peptide upstream of hGH were the whole prepro-peptide following the NH2-terminal region of mature MPR in JGH1, the intact pre-sequence and a part of the pro-sequence in JGH2, and the putative signal sequences of the NH2-terminal 18 and 22 amino acids in JGH3 and JGH7, respectively. When the hGH genes fused to these leader sequences were expressed in yeast cells under the control of the yeast GAL7 promoter, proteins of various sizes immunoreactive with the anti-hGH antibody were secreted into the medium. Among the plasmids mentioned above, JGH2 directed the greatest secretion of the protein of 23 kilodaltons in size, which contained the expected NH2-terminal amino acid sequence of an additional eight amino acids derived from the pro-peptide of MPR. The addition of the GAL10 terminator downstream of the hGH gene in JGH2 resulted in a greater than three- to fivefold increase in the secretion, whereas the insertion of the GAL4 gene, which is a positive regulator for the GAL system, had no significant effect. The improved yield of the total protein of hGH secreted into the medium reached approximately 10 mg/liter.     

The prepro-peptide of Mucor rennin directs the secretion of human growth hormone by Saccharomyces cerevisiae.

An aspartic proteinase, Mucor pusillus rennin (MPR), of filamentous fungus Mucor pusillus, is efficiently secreted from a transformant of Saccharomyces cerevisiae containing the intact MPR gene. To test the usefulness of the MPR leader peptide in secretion of heterologous proteins from yeast cells, several plasmids encoding the fusion proteins composed of different parts of the NH2-terminal region of prepro-MPR and human growth hormone (hGH) were constructed. The parts of the leader peptide upstream of hGH were the whole prepro-peptide following the NH2-terminal region of mature MPR in JGH1, the intact pre-sequence and a part of the pro-sequence in JGH2, and the putative signal sequences of the NH2-terminal 18 and 22 amino acids in JGH3 and JGH7, respectively. When the hGH genes fused to these leader sequences were expressed in yeast cells under the control of the yeast GAL7 promoter, proteins of various sizes immunoreactive with the anti-hGH antibody were secreted into the medium. Among the plasmids mentioned above, JGH2 directed the greatest secretion of the protein of 23 kilodaltons in size, which contained the expected NH2-terminal amino acid sequence of an additional eight amino acids derived from the pro-peptide of MPR. The addition of the GAL10 terminator downstream of the hGH gene in JGH2 resulted in a greater than three- to fivefold increase in the secretion, whereas the insertion of the GAL4 gene, which is a positive regulator for the GAL system, had no significant effect. The improved yield of the total protein of hGH secreted into the medium reached approximately 10 mg/liter.