Isolation of heterothallic haploid and auxotrophic mutants of Schizosaccharomyces japonicus

The fission yeast Schizosaccharomyces japonicus var. japonicus belong to the genus Schizosaccharomyces, together with Schizosaccharomyces pombe, which has been well studied as a model organism. In contrast, Sz. japonicus is poorly characterized and genetic tools were yet to be developed. We here report the isolation of the heterothallic haploids NIG2017, NIG2025 and NIG2028, which were derivatives of a Sz. japonicus homothallic strain (NIG2008). Based on the genomic sequence of Sz. japonicus, released by the Broad Institute, we found that Sz. japonicus also possesses orthologues of the mating‐type genes of Sz. pombe; two mat‐M (?) and two mat‐P (+) genes. As expected, heterothallic strains were defective in one of the Sz. japonicus mat genes (mat^sj). We confirmed that NIG2017 and NIG2025 strains only expressed mRNA from the mat^sj‐P genes, while homothallic strains expressed both mat^sj‐M and mat^sj‐P. Although the NIG2028 strain expressed both gene products, mat^sj‐P was found mutated, which may have conferred the heterothallic phenotype of the mutant. Thus, we concluded that these were stable heterothallic strains. We designated NIG2017 and NIG2025 as h⁺ and NIG 2028 as h^?, respectively. We also found additional h^? strains (NIG5872 and NIG5873) that arose from the cross between NIG2017 and NIG2028 derivatives. In addition to that, we have constructed a ura4^sj‐deleted strain and an ade6^sj‐mutated strain. We used these heterothallic strains and the auxotroph strains to perform spore dissection analysis to determine the genetic distances between several loci, and found that the mating type loci and ade6^sj locus were linked to centromeres. Copyright © 2009 John Wiley & Sons, Ltd.     

Construction and characterization of a series of vectors for Schizosaccharomyces pombe

A set of vectors was created to allow cloning and expression studies in Schizosaccharomyces pombe. These vectors had a uniform backbone with an efficient Sz. pombe ARS, ARS3002, but different selectable markers--his3+, leu1+, ade6+ and ura4+. The vectors functioned efficiently as autonomously replicating plasmids that could also be converted into integrating vectors. The ura4+-containing vector was used to construct a Sz. pombe genomic library.     

A vector system for efficient and economical switching of a ura4+ module to three commonly used antibiotic marker cassettes in Schizosaccharomyces pombe

We describe here the development of a set of plasmid vectors that allow simple, efficient and economical switching of a ura4⁺ module in existing Schizosaccharomyces pombe strains to any of the three routinely used antibiotic marker cassettes, kanMX6, hphMX6 and natMX6. In principle, the applications of this system can also be extended to switching ura4⁺ for additional MX6 module‐based cassettes, such as bleMX6, as long as the antibiotic marker has been cloned into an ura4⁺ module‐switching vector. We illustrate the application of this set of vectors in exchange of the ura4⁺ marker in existing strains with three antibiotic marker cassettes with high efficiency. Copyright © 2015 John Wiley & Sons, Ltd.     

Mutational analysis of the gene for Schizosaccharomyces pombe RNase MRP RNA,mrp1, using plasmid shuffle by counterselection on canavanine

Reverse genetics in fission yeast is hindered by the lack of a versatile established plasmid shuffle system. In order to screen efficiently and accurately through plasmid-borne mutations in the essential gene for the RNA component of RNase MRP, mrp1, we have developed a system for plasmid shuffling in fission yeast using counterselection on canavanine. The system takes advantage of the ability of the Saccharomyces cerevisiae CAN1 gene to complement a Schizosaccharomyces pombe can1-1 mutation. Two general use plasmids were constructed that allow directional cloning and initial selection for histidine before counterselection by canavanine. The strain constructed for plasmid shuffling carries auxotrophic markers for ade6, leu1, ura4 and his3 along with the can1-1 mutation. Using this system we examined several partial deletions and point mutations in conserved nucleotides of Schizosaccharomyces pombe RNase MRP RNA for their ability to complement a chromosomal deletion of the mrp1 gene. The degree of background canavanine resistance as well as plasmid–plasmid recombination encountered in these experiments was sufficiently low to suggest that the system we have set up for counterselection by canavanine in fission yeast using multicopy plasmids will be widely useful.     

Construction of an insertion marker collection of Sz. japonicus (IMACS) for genetic mapping and a fosmid library covering its genome

Measuring relative genetic distances is one of the best ways to locate genetic loci. Here we report the construction of a strains set for genetic mapping in Schizosaccharomyces japonicus, which belongs to the genus Schizosaccharomyces together with the well‐studied fission yeast Sz. pombe. We constructed 29 strains that bear a positive‐negative selection marker at different loci. The marker was inserted every 500 kb in the genome of Sz. japonicus. Each marker thus becomes a ‘scale mark’ of a chromosome that behaves like a yardstick. By determining the genetic distances from the inserted markers, the relative location of a genomic mutation can be determined. We also constructed a fosmid library that covers an entire genome of Sz. japonicus. These tools together would facilitate identification and cloning of the gene. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of Na+/H+-antiporter gene closely related to the salt-tolerance of yeast Zygosaccharomyces rouxii

In order to clarify the relationship between salt-tolerance of Zygosaccharomyces rouxii and the function of Na⁺/H⁺-antiporter, a gene was isolated from Z. rouxii which exhibited homology to the Na⁺/H⁺-antiporter gene (sod2) from Schizosaccharomyces pombe. This newly isolated gene (Z-SOD2) encoded a product of 791 amino acids, which was larger than the product encoded by its Sz. pombe homologue. The predicted amino-acid sequence of Z-Sod2p was highly homologous to that of the Sz. pombe protein, but included an extra-hydrophilic stretch in the C-terminal region. The expression of Z-SOD2 was constitutive and independent of NaCl-shock. Z-SOD2-disruptants of Z. rouxii did not grow in media supplemented with 3 M -NaCl, but grew well in the presence of 50% sorbitol, indicating that the function of Z-SOD2 was closely related to the salt-tolerance of Z. rouxii. Several genes are also compared and discussed in relation to the salt-tolerance of Z. rouxii. The nucleotide sequence data reported in this paper will appear in the GSDB, DDBJ, EMBL and NCBI nucleotide sequence databases with the following accession number: D43629.     

Heterologous modules for efficient and versatile PCR-based gene targeting in Schizosaccharomyces pombe

We describe a straightforward PCR-based approach to the deletion, tagging, and overexpression of genes in their normal chromosomal locations in the fission yeast Schizosaccharomyces pombe. Using this approach and the S. pombe ura4⁺ gene as a marker, nine genes were deleted with efficiencies of homologous integration ranging from 6 to 63%. We also constructed a series of plasmids containing the kanMX6 module, which allows selection of G418-resistant cells and thus provides a new heterologous marker for use in S. pombe. The modular nature of these constructs allows a small number of PCR primers to be used for a wide variety of gene manipulations, including deletion, overexpression (using the regulatable nmt1 promoter), C- or N-terminal protein tagging (with HA, Myc, GST, or GFP), and partial C- or N-terminal deletions with or without tagging. Nine genes were manipulated using these kanMX6 constructs as templates for PCR. The PCR primers included 60 to 80 bp of flanking sequences homologous to target sequences in the genome. Transformants were screened for homologous integration by PCR. In most cases, the efficiency of homologous integration was ≥50%, and the lowest efficiency encountered was 17%. The methodology and constructs described here should greatly facilitate analysis of gene function in S. pombe. © 1998 John Wiley & Sons, Ltd.     

Gene disruption in Schizosaccharomyces pombe using a temperature‐sensitive Ura4p

We have generated a temperature‐sensitive form of the Ura4p protein from the fission yeast Schizosaccharomyces pombe. A single T‐to‐C mutation at nucleotide 782 (relative to the initiator ATG codon of ura4) changes the leucine residue at position 261 in Ura4p to a proline. The mutant Ura4p^ts supports growth at 30°C but is unable to allow growth at 37°C in the absence of uracil when a single copy of the gene is integrated into the host chromosome. Using the ura4^ts cassette for gene replacements simplifies the identification of transformants in which the disruption construct has undergone homologous integration into the host chromosome, as these individuals contain a single copy of the ura4^ts gene and fail to grow when replicated to 37°C in the absence of uracil. Copyright © 1999 John Wiley & Sons, Ltd.     

Plasmids with E2 epitope tags: tagging modules for N‐ and C‐terminal PCR‐based gene targeting in both budding and fission yeast,and inducible expression vectors for fission yeast

A single‐step PCR‐based epitope tagging enables fast and efficient gene targeting with various epitope tags. This report presents a series of plasmids for the E2 epitope tagging of proteins in Saccharomyces cerevisiae and Schizosaccharomyces pombe. E2Tags are 10‐amino acids (epitope E2a: SSTSSDFRDR)‐ and 12 amino acids (epitope E2b: GVSSTSSDFRDR)‐long peptides derived from the E2 protein of bovine papillomavirus type 1. The modules for C‐terminal tagging with E2a and E2b epitopes were constructed by the modification of the pYM‐series plasmid. The N‐terminal E2a and E2b tagging modules were based on pOM‐series plasmid. The pOM‐series plasmids were selected for this study because of their use of the Cre–loxP recombination system. The latter enables a marker cassette to be removed after integration into the loci of interest and, thereafter, the tagged protein is expressed under its endogenous promoter. Specifically for fission yeast, high copy pREP plasmids containing the E2a epitope tag as an N‐terminal or C‐terminal tag were constructed. The properties of E2a and E2b epitopes and the sensitivity of two anti‐E2 monoclonal antibodies (5E11 and 3F12) were tested using several S. cerevisiae and Sz. pombe E2‐tagged strains. Copyright © 2009 John Wiley & Sons, Ltd.     

Heterologous HIS3 Marker and GFP Reporter Modules for PCR-Targeting in Saccharomyces cerevisiae

We have fused the open reading frames of his3-complementing genes from Saccharomyces kluyveri and Schizosaccharomyces pombe to the strong TEF gene promotor of the filamentous fungus Ashbya gossypii. Both chimeric modules and the cognate S. kluyveri HIS3 gene were tested in transformations of his3 S. cerevisiae strains using PCR fragments flanked by 40 bp target guide sequences. The 1·4 kb chimeric Sz. pombe module (HIS3MX6) performed best. With less than 5% incorrectly targeted transformants, it functions as reliably as the widely used geniticin resistance marker kanMX. The rare false-positive His⁺ transformants seem to be due to non-homologous recombination rather than to gene conversion of the mutated endogenous his3 allele. We also cloned the green fluorescent protein gene from Aequorea victoria into our pFA-plasmids with HIS3MX6 and kanMX markers. The 0·9 kb GFP reporters consist of wild-type GFP or GFP-S65T coding sequences, lacking the ATG, fused to the S. cerevisiae ADH1 terminator. PCR-synthesized 2·4 kb-long double modules flanked by 40–45 bp-long guide sequences were successfully targeted to the carboxy-terminus of a number of S. cerevisiae genes. We could estimate that only about 10% of the transformants carried inactivating mutations in the GFP reporter. © 1997 by John Wiley & Sons, Ltd.     

Properties and Heterologous Expression of the Glucose Transporter GHT1 from Schizosaccharomyces pombe

Genomic DNA of the Schizosaccharomyces pombe glucose transporter, GHT1, was obtained by complementation of the glucose transport deficient Sz. pombe strain YGS-5. Here we describe the GHT1 gene that encodes a protein of 565 amino acids with a corresponding molecular mass of 62·5 kDa. This eukaryotic glucose transporter contains 12 putative transmembrane segments and is homologous to the HXT multigene family of S. cerevisiae with several amino acid motifs of this sugar transporter family. It is also homologous to other sugar carriers from human, mouse and Escherichia coli. The function of the Ght1 protein as a glucose transporter was proved both by homologous and heterologous expression in the Sz. pombe mutant YGS-5 and in the S. cerevisiae hxt mutant RE700A, respectively. Both transformed yeast strains transported d -glucose with substrate specificity similar to that in Sz. pombe wild-type cells. Moreover, the cells of the two transformed yeast strains accumulated 2-deoxy-d -glucose, a non-metabolizable d -glucose analogue, with an efficiency similar to Sz. pombe wild-type cells. The ability of the S. cerevisiae mutant RE700A to accumulate 2DG in an Δμdependent manner after transformation with GHT1 provides evidence that the Sz. pombe transporter catalyses an energy-dependent uptake of glucose. The sequence of GHT1 was deposited at EMBL, Outstation EBI, Accession Number X91218. ©1997 John Wiley & Sons, Ltd.     

Efficient electropulse transformation of intact Candida maltosa cells by different homologous vector plasmids.

Conditions for efficient and quick transformation by electroporation were developed in Candida maltosa. To investigate the efficiency of transformation with integrative as well as with autonomously replicating plasmids, a series of vectors was constructed for homologous transformation of this species. Transformants were obtained with different plasmids as covalently closed circular molecules and as linearized DNA. The influence of recipient strain and plasmid type as well as of cell number and parameters of the supplied electrical pulse on the transformation efficiency have been investigated. A maximum of 7000 transformants per 100 ng of plasmid DNA was reached. The efficiency of transformation was compared with that of the LiCl method.     

New cassettes for single‐step drug resistance and prototrophic marker switching in fission yeast

Construction of multiply mutated strains for genetic interaction analysis and of strains carrying different epitope tags at multiple open reading frames for testing protein localization, abundance and protein–protein interactions is hampered by the availability of a sufficient number of different selectable markers. Moreover, strains with single gene deletions or tags often already exist in strain collections; for historical reasons these will mostly carry the ura4⁺ gene or the G418‐resistance kanMX as marker. Because it is rather cumbersome to produce multiply deleted or tagged strains using the same marker, or to completely reconstruct a particular strain with a different marker, single‐step exchange protocols of markers are a time‐saving alternative. In recent years, dominant drug resistance markers (DDRMs) against clonNAT, hygromycin B and bleomycin have been adapted and successfully used in Schizosaccharomyces pombe. The corresponding DDRM cassettes, natMX, hphMX and bleMX, carry the TEF promotor and terminator sequences from Ashbya gossypii as kanMX; this provides flanking homologies to enable single‐step marker swapping by homologous gene targeting. To expand this very useful toolset for single‐step marker exchange, I constructed MX cassettes containing the nutritional markers arg3⁺, his3⁺, leu1⁺ and ura4⁺. Furthermore, a set of constructs was created to enable single‐step exchange of ura4⁺ to kanMX6, natMX4 and hphMX4. The functionality of the cassettes is demonstrated by successful single‐step marker swapping at several loci. These constructs allow straightforward and rapid remarking of existing ura4⁺‐ and MX‐deleted and ‐tagged strains. Copyright © 2015 John Wiley & Sons, Ltd.     

Molecular cloning of the plc1+ gene of Schizosaccharomyces pombe,which encodes a putative phosphoinositide-specific phospholipase C

Exploiting the polymerase chain reaction, we have isolated a gene that encodes a putative phosphoinositide-specific phospholipase C (PLC) of the fission yeast Schizosaccharomyces pombe. Inspection of the nucleotide sequence of the gene revealed an open reading frame that can encode a polypeptide of 899 amino acid residues with a calculated molecular mass of 102 kDa. This putative polypeptide contains both the X and Y regions that are conserved among three classes of mammalian PLC, and also contains a presumptive Ca²⁺-binding site (an E-F hand motif). The structure of the putative protein is most similar to that of the δ class of PLC isozymes. To investigate the role of this gene, designated plc1⁺, gene disruption was carried out by interrupting the coding region with the ura4⁺ marker. Growth of plc1 cells was temperature-sensitive in rich medium, and cells could not grow in synthetic medium. Expression of the PLC1 gene of Saccharomyces cerevisiae suppressed the growth defect phenotype of plc1^? cells, a strong suggestion that the plc1⁺ gene encodes PLC. The PLC1 sequence appears in the public data libraries, DDBJ GenBank, EMBL under the following Accession Number: D38309.     

Essential role of Ubr11, but not Ubr1, as an N‐end rule ubiquitin ligase in Schizosaccharomyces pombe

The N‐end rule pathway degrades proteins bearing a destabilization‐inducing amino acid at the N‐terminus. In this proteolytic system, Ubr ubiquitin ligases recognize and ubiquitylate substrates intended for degradation. Schizosaccharomyces pombe has two similar Ubr proteins, Ubr1 and Ubr11. Both proteins have unique roles in various cellular processes, although the ubr1? strain shows more severe defects. However, their involvement in the N‐end rule pathway is unclear, and even the N‐end rule pathway‐dependent proteolytic activity has not been demonstrated in Sz. pombe. Here, we show that: (a) Sz. pombe has the N‐end rule pathway in which only Ubr11, but not Ubr1, is responsible; and (b) the C‐terminal fragment of the meiotic cohesin Rec8 (denoted as Rec8c) generated by separase‐mediated cleavage is an endogenous substrate of the N‐end rule pathway. Forced overexpression of stable Rec8c was deleterious in mitosis and caused a loss of the mini‐chromosome. In unperturbed mitosis without overexpression, the rate of mini‐chromosome loss was five‐fold higher in the ubr11? strain. Since Rec8 is normally produced in meiosis, we examined whether meiosis and sporulation were affected in the ubr11? strain. In unperturbed meiosis, chromosome segregation occurred almost normally and viable spores were produced in the ubr11? cells, irrespective of the presence of undegraded endogenous Rec8c peptides. Copyright © 2012 John Wiley & Sons, Ltd.     

Construction of an autonomously replicating plasmid in n-alkane-assimilating yeast, Candida tropicalis

A transformation system using the autonomously replicating plasmid in the n-alkane-assimilating and asporogenic diploid yeast, Candida tropicalis, was developed. For the cloning of a DNA fragment containing a potential autonomously replicating sequence (ARS) from the genomic DNA of C. tropicalis, the ura3 mutant obtained using ethylmethane sulfonate as the host and the URA3 gene amplified by PCR using the C. tropicalis genomic DNA as a selectable marker were prepared. Comparison of ARSs among yeasts revealed that the consensus sequence found in S. cerevisiae was also present in C. tropicalis. The autonomously replicating plasmid containing the putative ARS as the shuttle vector, capable of replicating in both E. coli and C. tropicalis, was first constructed. The transformation system using this plasmid, in addition to the integrative transformation system, will be applicable to genetic studies of C. tropicalis.     

Non‐homologous end joining‐mediated functional marker selection for DNA cloning in the yeast Kluyveromyces marxianus

The cloning of DNA fragments into vectors or host genomes has traditionally been performed using Escherichia coli with restriction enzymes and DNA ligase or homologous recombination‐based reactions. We report here a novel DNA cloning method that does not require DNA end processing or homologous recombination, but that ensures highly accurate cloning. The method exploits the efficient non‐homologous end‐joining (NHEJ) activity of the yeast Kluyveromyces marxianus and consists of a novel functional marker selection system. First, to demonstrate the applicability of NHEJ to DNA cloning, a C‐terminal‐truncated non‐functional ura3 selection marker and the truncated region were PCR‐amplified separately, mixed and directly used for the transformation. URA3⁺ transformants appeared on the selection plates, indicating that the two DNA fragments were correctly joined by NHEJ to generate a functional URA3 gene that had inserted into the yeast chromosome. To develop the cloning system, the shortest URA3 C‐terminal encoding sequence that could restore the function of a truncated non‐functional ura3 was determined by deletion analysis, and was included in the primers to amplify target DNAs for cloning. Transformation with PCR‐amplified target DNAs and C‐terminal truncated ura3 produced numerous transformant colonies, in which a functional URA3 gene was generated and was integrated into the chromosome with the target DNAs. Several K. marxianus circular plasmids with different selection markers were also developed for NHEJ‐based cloning and recombinant DNA construction. The one‐step DNA cloning method developed here is a relatively simple and reliable procedure among the DNA cloning systems developed to date. Copyright © 2013 John Wiley & Sons, Ltd.     

YHp as a highly stable,hyper-copy,hyper-expression plasmid constructed using a full 2-μm circle sequence in cir0 strains of Saccharomyces cerevisiae

In the yeast Saccharomyces cerevisiae, the yeast episomal plasmid (YEp), containing a partial sequence from a natural 2-μm plasmid, has been frequently used to induce high levels of gene expression. In this study, we used Japanese sake yeast natural cir⁰ strain as a host for constructing an entire 2-μm plasmid with an expression construct using the three-fragment gap-repair method without Escherichia coli manipulation. The 2-μm plasmid contains two long inverted repeats, which is problematic for the amplification by polymerase chain reaction. Therefore, we amplified it by dividing into two fragments, each containing a single repeat together with an overlapping sequence for homologous recombination. TDH3 promoter-driven yEmRFP (TDH3p-yEmRFP) and the URA3 were used as a reporter gene and a selection marker, respectively, and inserted at the 3′ end of the RAF1 gene on the 2-μm plasmid. The three fragments were combined and used for the transformation of sake yeast cir⁰ ura3^- strain. The resulting transformant colonies showed a red or purple coloration, which was significantly stronger than that of the cells transformed with YEp-TDH3p-yEmRFP. The 2-μm transformants were cultured in YPD medium and observed by fluorescence microscopy. Almost all cells showed strong fluorescence, suggesting that the plasmid was preserved during nonselective culture conditions. The constructed plasmid maintained a high copy state similar to that of the natural 2-μm plasmid, and the red fluorescent protein expression was 54 fold compared with the chromosomal integrant. This vector is named YHp, the Yeast Hyper expression plasmid.     

Vectors for gene expression and amplification in the yeast Yarrowia lipolytica

New vector systems were developed for gene expression in Y. lipolytica. These plasmids contain: (a) as integration target sequences, either a rDNA region or the long terminal repeat zeta of the Y. lipolytica retrotransposon Ylt1; (b) the YlURA3 gene as selection marker for Y. lipolytica, either as the non-defective ura3d1 allele for single integration or the promotor truncated ura3d4 allele for multiple integration; (c) the inducible ICL1 or XPR2 promoters for gene expression; and (d) unique restriction sites for gene insertion. Multiple plasmid integration occurred as inserted tandem-repeats, which are present at 3-39 copies per cell. A correlation between gene copy number and the expressed enzyme activity was demonstrated with Escherichia coli lacZ as reporter gene under the control of the regulated ICL1 promoter. Increases in copy numbers from 5 to 13 for the lacZ expression cassettes resulted in an up to 10-11-fold linear increase of the beta-galactosidase activity in multicopy transformants during their growth on ethanol or glucose, compared with the low-copy replicative plasmid transformants (1.6 plasmid copies). These new tools will enhance the interest in Y. lipolytica as an alternative host for heterologous protein production.