Cloning of the blasticidin S deaminase gene (BSD) from Aspergillus terreus and its use as a selectable marker for Schizosaccharomyces pombe and Pyricularia oryzae

Aspergillus terreus produces a unique enzyme, blasticidin S deaminase, which catalyzes the deamination of blasticidin S (BS), and in consequence confers high resistance to the antibiotic. A cDNA clone derived from the structural gene for BS deaminase (BSD) was isolated by transforming Escherichia coli with an Aspergillus cDNA expression library and directly selecting for the ability to grow in the presence of the antibiotic. The complete nucleotide sequene of BSD was determined and proved to contain an open reading frame of 393 bp, encoding a polypeptide of 130 amino acids. Comparison of its nulceotide sequence with that of bsr, the BS deaminase gene isolated from Bacillus cereus, indicated no homology and a large difference in codon usage. The activity of BSD expressed in E. coli was easily quantified by an assay based on spectrophotometric recording. The BSD gene was placed in a shuttle vector for Schizosaccharomyces pombe, downstream of the SV40 early region promoter, and this allowed direct selection with BS at high frequency, following transformation into the yeast. The BSD gene was also employed as a selectable marker for Pyricularia oryzae, which could not be transformed to BS resistance by bsr. These results promise that the BSD gene will be useful as a new dominant selectable marker for eukaryotes.     

Cloning of the blasticidin S deaminase gene (BSD) from Aspergillus terreus and its use as a selectable marker for Schizosaccharomyces pombe and Pyricularia oryzae

Aspergillus terreus produces a unique enzyme, blasticidin S deaminase, which catalyzes the deamination of blasticidin S (BS), and in consequence confers high resistance to the antibiotic. A cDNA clone derived from the structural gene for BS deaminase (BSD) was isolated by transforming Escherichia coli with an Aspergillus cDNA expression library and directly selecting for the ability to grow in the presence of the antibiotic. The complete nucleotide sequene of BSD was determined and proved to contain an open reading frame of 393 bp, encoding a polypeptide of 130 amino acids. Comparison of its nulceotide sequence with that of bsr, the BS deaminase gene isolated from Bacillus cereus, indicated no homology and a large difference in codon usage. The activity of BSD expressed in E. coli was easily quantified by an assay based on spectrophotometric recording. The BSD gene was placed in a shuttle vector for Schizosaccharomyces pombe, downstream of the SV40 early region promoter, and this allowed direct selection with BS at high frequency, following transformation into the yeast. The BSD gene was also employed as a selectable marker for Pyricularia oryzae, which could not be transformed to BS resistance by bsr. These results promise that the BSD gene will be useful as a new dominant selectable marker for eukaryotes.     

Over expression of the selectable marker blasticidin S deaminase gene is toxic to human keratinocytes and murine BALB/MK cells

Background  

The blasticidin S resistance gene (bsr) is a selectable marker used for gene transfer experiments. The bsr gene encodes for blasticidin S (BS) deaminase, which has a specific activity upon BS. Therefore, its expression is supposed to be harmless in cells. The work reported on herein consisted of experiments to verify a possible toxicity of bsr on mammalian cells, which include several cell lines and primary cultures.     

稻瘟净（Blasticidin S）脱氨酶基因的克隆

从一株抗稻瘟净（ＢＳ）的Ａｓｐｅｒｇｉｌｌｕｓ ｔｅｒｒｅｕｓ菌中克隆到一个ｂｌａｓｔｉｅｉｄｉｎＳ脱氨酶基因,命名为ｂｓｒＡＳ。ＤＮＡ序列分析表明ｂｓｒＡＳ不含内含子。编码区长３９０ｂｐ,编码１３０个氨基酸。将ｂｓｒＡＳ转化到稻瘟菌中,能使受体菌表达出ＢＳ脱氨酶的活性,从而产生抗药性。该基因可作为抗药标记基因使用,建立稻瘟菌的基因转化系统。     

Modified blasticidin S resistance gene (bsrm) as a selectable marker for construction of retroviral vectors

Retroviral vectors are commonly used in ex vivo gene therapy protocols. The structure of vectors basically consists of one gene of interest and a selectable marker gene. Fast selection without damaging cells is a critical step for ex vivo gene therapy protocols. Blasticidin S deaminase isolated from Bacillus cereus has a neutralizing action on the highly toxic antibiotic blasticidin S (BS). A commercially available gene coding for blasticidin S deaminase (bsr) when used to construct retroviral vectors, LBSN and LNSB, provided very low levels of BS deaminase activity, precluding their routine use in gene transfer experiments. However, with the introduction of specific mutations into the bsr gene based on the Kozak consensus sequences and deletion of a 5' untranslated sequence to generate bsrm, we were able to construct a retroviral vector encoding resistance to high doses of BS (at least 16-fold above the usual lethal dose in NIH3T3 cells), showing that bsrm/BS may provide a useful system for selection of transduced mammalian cells.     

Blasticidin S-resistance gene (bsr): a novel selectable marker for mammalian cells.

Blasticidin S is a microbial antibiotic that inhibits protein synthesis in both prokaryotes and eukaryotes. The blasticidin S-resistance gene (bsr), isolated from Bacillus cereus K55-S1 strain, was inserted into pSV2 plasmid vector and introduced into cultured mammalian cells by transfection. The bsr gene was integrated into the genome and conferred blasticidin S resistance on HeLa cells. The transfection frequency of the bsr gene was as high as that of the aminoglycoside phosphotransferase gene, the so-called neo gene, which is a representative selectable marker for mammalian cells. Transfectants in which several copies of bsr had been integrated into the genome were highly resistant to blasticidin S. Furthermore, blasticidin S killed the cells more rapidly than G418, which is conventionally used as a selective drug for the neo gene. Thus bsr is concluded to be useful as a drug-resistance marker for mammalian cells.     

Separation and characterization of six (1 leads to 3)-beta-glucanases from Saccharomyces cerevisiae.

Using a system of chromatography through columns of DEAE-Bio-Gel, HTP-Bio-Gel, and CM-Bio-Gel, we isolated and characterized six different (1 leads to 3)-beta-glucanases from cell wall autolysates and cell extracts of Saccharomyces cerevisiae haploid strain 2180B. These enzymes were designated glucanases I, II, IIIA, IIIB, IV, and V. The haploid mating type S. cerevisiae strain 2180A and the diploid strains S. cerevisiae 2180D and S. cerevisiae 595 contained the same complex of glucanases. Glucanases II and IIIA were exoenzymes, and glucanases I, IIIB, IV, and V were endoenzymes. The enzymes exhibited different molecular weights, kinetic properties, and activities on isolated yeast cell walls. The products of substrate (laminarin) hydrolysis were quantified by using high-pressure liquid chromatography and were significantly different for the four endoglucanases.     

Characterization of maltotriose transporters from the Saccharomyces eubayanus subgenome of the hybrid Saccharomyces pastorianus lager brewing yeast strain Weihenstephan 34/70

The genome from the Saccharomyces pastorianus industrial lager brewing strain Weihenstephan 34/70, a natural Saccharomyces cerevisiae/Saccharomyces eubayanus hybrid, indicated the presence of two different maltotriose transporter genes: a new gene in the S. eubayanus subgenome with 81% of homology to the AGT1 permease from S. cerevisiae, and an amplification of the S. eubayanus MTY1 maltotriose permease previously identified in S. pastorianus yeasts. To characterize these S. eubayanus transporter genes, we used a S. cerevisiae strain deleted in the AGT1 permease and introduced the desired permease gene(s) into this locus through homologous recombination. Our results indicate that both the MTY1 and AGT1 genes from the S. eubayanus subgenome encode functional maltotriose transporters that allow fermentation of this sugar by yeast cells, despite their apparent differences in the kinetics of maltotriose‐H⁺ symport activity. The presence of two maltotriose transporters in the S. eubayanus subgenome not only highlights the importance of sugar transport for efficient maltotriose utilization by industrial yeasts, but these new genes can be used in breeding and/or selection programs aimed at increasing yeast fitness for the efficient fermentation of brewer's wort.     

Five novel species of the anamorphic genus Candida in the Cyberlindnera clade isolated from natural substrates in Taiwan

Twelve strains representing five novel yeast species were isolated from natural samples distributed in mountain areas in Taiwan during 2007 and 2009. Sequence analysis of the D1/D2 domain of the large subunit (LSU) rRNA gene revealed that these species are members of the Cyberlindnera clade. These five new species have a greater than 1% difference from their closest relatives in the sequences of the D1/D2 domain of the LSU rRNA gene and were well separated from their closest relatives in terms of physiological characteristics. Moreover, a sexual state could not be found in these five novel yeast species. Therefore, the scientific names of Candida maesa sp. nov. (type strain GJ8L01^T), Candida takata sp. nov. (type strain EN25S01^T), Candida taoyuanica sp. nov. (type strain GY15S07^T), Candida hungchunana sp. nov. (type strain NC3W71^T) and Candida stauntonica sp. nov. (type strain GY13L05^T) were proposed to accommodate these yeasts.     

Novel strategy for yeast construction using δ-integration and cell fusion to efficiently produce ethanol from raw starch

We developed a novel strategy for constructing yeast to improve levels of amylase gene expression and the practical potential of yeast by combining δ-integration and polyploidization through cell fusion. Streptococcus bovis α-amylase and Rhizopus oryzae glucoamylase/α-agglutinin fusion protein genes were integrated into haploid yeast strains. Diploid strains were constructed from these haploid strains by mating, and then a tetraploid strain was constructed by cell fusion. The α-amylase and glucoamylase activities of the tetraploid strain were increased up to 1.5- and tenfold, respectively, compared with the parental strain. The diploid and tetraploid strains proliferated faster, yielded more cells, and fermented glucose more effectively than the haploid strain. Ethanol productivity from raw starch was improved with increased ploidy; the tetraploid strain consumed 150 g/l of raw starch and produced 70 g/l of ethanol after 72 h of fermentation. Our strategy for constructing yeasts resulted in the simultaneous overexpression of genes integrated into the genome and improvements in the practical potential of yeasts.     

Mutant isolation of non-urea producing sake yeast by positive selection

Urea is reported to be a main precursor in wine and sake (Japanese rice wine) of ethyl carbamate (ECA), a suspected carcinogen. We constructed an arginase-deficient mutant (Δcar1/Δcar1) from a diploid sake yeast, Kyokai no. 9, using a gene disruption method (Kitamoto, K. et al., Appl. Environ. Microbiol., 57, 301, 1991). The car1 mutant thus constructed enabled us to brew sake containing no urea or ECA. In spite of their superior characteristics, industrial use of mutants for sake brewing has so far been difficult because guidelines for recombinant DNA utilization in the food and beverages industry have not yet been established. Using the genetically engineered car1 mutant, we have developed a new medium for the positive selection of car1 mutants. Many arginase-deficient mutants could be easily isolated from not only a laboratory haploid strain (X2180-1A), but also sake yeasts (Kyokai no. 9 and Kyokai no 10) and wine yeasts (Geisenheim 74 and Eperney). Sake with no urea could be brewed using the car1 mutants, and no ECA was detected in the resulting sake even after heat treatment (hi-ire) and storage.     

Stable transformation of trypanosomatids through targeted chromosomal integration of the selectable marker gene encoding blasticidin S deaminase

The susceptibilities of the protozoan parasites Leishmania mexicana and Trypanosoma brucei to the nucleoside antibiotic blasticidin S were assessed. A concentration of 10 microg ml(-1) was sufficient to cause cell death within 72 h of L. mexicana promastigotes and bloodstream forms of T. brucei in vitro. The gene encoding blasticidin S deaminase (BSD) was therefore incorporated into cassettes for targeting to the cysteine proteinase C locus of L. mexicana (CPC::BSD) and the tubulin locus of T. brucei (tub::RAD51-BSR). Following transfection of mutant parasites that contained other well-established selectable marker genes (HYG, NEO, BLE, PAC and SAT), clones resistant to 10 microg ml(-1) blasticidin S were shown by PCR and Southern blotting to have integrated the cassettes by homologous recombination. The results confirm that BSD can be used as a selectable marker gene for targeted chromosomal integration during genetic manipulations of trypanosomatids.     

Construction of a Stable α-Galactosidase-Producing Baker's Yeast Strain

Molasses is widely used as a substrate for commercial yeast production. The complete hydrolysis of raffinose, which is present in beet molasses, by Saccharomyces strains requires the secretion of α-galactosidase, in addition to the secretion of invertase. Raffinose is not completely utilized by commercially available yeast strains used for baking, which are Mel⁻. In this study we integrated the yeast MEL1 gene, which codes for α-galactosidase, into a commercial mel⁰ baker's yeast strain. The Mel⁺ phenotype of the new strain was stable. The MEL1 gene was expressed when the new Mel⁺ baker's yeast was grown in molasses medium under conditions similar to those used for baker's yeast production at commercial factories. The α-galactosidase produced by this novel baker's yeast strain hydrolyzed all the melibiose that normally accumulates in the growth medium. As a consequence, additional carbohydrate was available to the yeasts for growth. The new strain also produced considerably more α-galactosidase than did a wild-type Mel⁺ strain and may prove useful for commercial production of α-galactosidase.     

Inhibition of the M r 70,000 S6 kinase pathway by rapamycin results in chromosome malsegregation in yeast and mammalian cells

The antifungal and immunosuppressive drug rapamycin arrests the cell cycle in G1-phase in both yeast and mammalian cells. In mammalian cells, rapamycin selectively inhibits phosphorylation and activation of p70 S6 kinase (p70^S6K), a protein involved in the translation of a subset of mRNAs, without affecting other known kinases. We now report that rapamycin causes chromosome malsegregation in mammalian and yeast cells. Chromosome malsegregation was determined by metaphase chromosome analysis of human lymphocytes and lymphoblasts, detection of CREST-positive micronuclei in human lymphoblasts and Chinese hamster embryonic fibroblast (CHEF) cells, and selection of doubly prototrophic cells in a specially constructed yeast strain. The number of ana-telophases with displaced chromosomes and interphase and mitotic cells with an irregular number of centrosomes was also determined in CHEF cells. In quiescent mammalian cells (human lymphocytes and CHEF cells) induced with growth factor to re-enter the cell cycle, rapamycin was effective when cells were exposed at the time of p70^S6K activation. In yeast, rapamycin was more effective when treatment was started in G1- than in G2-synchronized cells. Cells from ataxia telangiectasia (A-T) patients are characterized by chromosome instability and have recently been found to be resistant to the growth-inhibiting effect of rapamycin. We found that an A-T lymphoblastoid cell line was also resistant to the induction of chromosome malsegregation by rapamycin, but the level of spontaneous aneuploidy was higher than in normal cells. In yeast, the induction of chromosome malsegregation was dependent on the presence of a wild-type TUB2 gene, encoding the β-subunit of tubulin. The finding that rapamycin acts in different cell types and organisms suggests that the drug affects a conserved step important for proper segregation of chromosomes. One or more proteins required for chromosome segregation could be under the control of the rapamycin-sensitive pathway. Received: 3 August 1998 / Accepted: 20 August 1998     

A comparison of stress tolerance in YPD and industrial lignocellulose-based medium among industrial and laboratory yeast strains

In general, it is believed that fermentation by yeast under harsh industrial conditions, especially if substrates such as wood hydrolysate or lignocellulosic substrates are used, requires the use of so-called industrial strains. In order to check whether this is always true, a comparison of performance was made using two industrial strains and four commonly used laboratory strains, the haploid and diploid versions of CEN-PK and X2180, under industrially relevant stress conditions. The industrial strains were a Swedish commercial baker’s yeast strain and a strain previously isolated from an industrial bioethanol production plant using lignocellulosic substrate. Stress conditions included, apart from growth in the lignocellulosic substrate itself, elevated concentrations of glucose, NaCl, ethanol, and lactate as well as low pH. Results showed that, indeed, the strain adapted to lignocellulosic substrate also possessed the highest growth rate as well as shortest duration of the lag phase in this type of medium. However, the higher the additional stress level, the lower the difference compared to other strains, and X2180 in particular displayed a high resistance to these additional stress conditions. Furthermore, no difference in performance could be detected between the haploid or diploid versions of the laboratory strains. It might be that, at least under some circumstances, a laboratory strain such as X2180 could be an industrially attractive production organism with the advantage of facilitating the possibilities for making controlled genetic manipulations.     

Transformation of Sexually Transmitted Infection-Causing Serovars of Chlamydia trachomatis Using Blasticidin for Selection

Plasmid-free Chlamydia trachomatis serovar L2 organisms have been transformed with chlamydial plasmid-based shuttle vectors pGFP::SW2 and pBRCT using β-lactamase as a selectable marker. However, the recommendation of amoxicillin, a β-lactam antibiotics, as one of the choices for treating pregnant women with cervicitis due to C. trachomatis infection has made the existing shuttle vectors unsuitable for transforming sexually transmitted infection (STI)-causing serovars of C. trachomatis. Thus, in the current study, we modified the pGFP::SW2 plasmid by fusing a blasticidin S deaminase gene to the GFP gene to establish blasticidin resistance as a selectable marker and replacing the β-lactamase gene with the Sh ble gene to eliminate the penicillin resistance. The new vector termed pGFPBSD/Z::SW2 was used for transforming plasmid-free C. trachomatis serovar D organisms. Using blasticidin for selection, stable transformants were obtained. The GFP-BSD fusion protein was detected in cultures infected with the pGFPBSD/Z::SW2-trasnformed serovar D organisms. The transformation restored the plasmid property to the plasmid-free serovar D organisms. Thus, we have successfully modified the pGFP::SW2 transformation system for studying the biology and pathogenesis of other STI-causing serovars of C. trachomatis.     

Expression of theSaccharomyces cerevisiae MPR1 gene encodingN-acetyltransferase inZygosaccharomyces rouxii confers resistance tol-azetidine-2-carboxylate

The osmotolerant yeast Zygosaccharomyces rouxii is sensitive to the toxic L-proline analogue, L-azetidine-2-carboxylate (AZC). The possibility of use of the Saccharomyces cerevisiae MPR1 gene (ScMPR1) encoding the AZC-detoxifying enzyme as a dominant selection marker in Z. rouxii was examined. The heterologous expression of ScMPR1 in two Z. rouxii strains resulted in AZC-resistant colonies, but that of ScMPR1 as a dominant marker gene in vectors was affected by a high frequency of spontaneously resistant colonies. The same was found for an AZC-sensitive S. cerevisiae strain in which the ScMPR1 was expressed. In both yeasts, ScMPR1 can be used only as an auxiliary marker gene.     

Isolation of Auxotrophic Mutants of Diploid Industrial Yeast Strains after UV Mutagenesis

Auxotrophic mutants of the yeast Saccharomyces cerevisiae are usually isolated in haploid strains because the isolation of recessive mutations in diploids is thought to be difficult due to the presence of two sets of genes. We show here that auxotrophic mutants of diploid industrial sake yeast strains were routinely obtained by a standard mutant selection procedure following UV mutagenesis. We isolated His⁻, Met⁻, Lys⁻, Trp⁻, Leu⁻, Arg⁻, and Ura⁻ auxotrophic mutants of five sake strains, Kyokai no. 7, no. 9, no. 10, no. 701, and no. 901, by screening only 1,700 to 3,400 colonies from each treated strain. Wild-type alleles were cloned and used as markers for transformation. With HIS3 as a selectable marker, the yeast TDH3 overexpression promoter was inserted upstream of ATF1, encoding alcohol acetyltransferase, by one-step gene replacement in a his3 mutant of Kyokai no. 7. The resulting strain contained exclusively yeast DNA, making it acceptable for commercial use, and produced a larger amount of isoamyl acetate, a banana-like flavor. We argue that the generally recognized difficulty of isolating auxotrophic mutants of diploid industrial yeast strains is misleading and that genetic techniques used for haploid laboratory strains are applicable for this purpose.     

Genome-wide expression profile of sake brewing yeast under shaking and static conditions

To identify the genes responsible for characteristics, that are different as between sake brewing yeasts and laboratory yeast strains, we used a DNA microarray to compare the genome-wide gene expression profiles of a sake yeast, Saccharomyces cerevisiae K-9 (kyokai 9), and a laboratory yeast, S. cerevisiae X2180-1A, under shaking and static conditions.The genes overexpressed in K-9 more than in X2180-1A were related to C-metabolism, including the HXT, ATP, and COX genes, ergosterol biosynthesis, ERG genes, and thiamine metabolism, THI genes. These genes may contribute to higher growth rates and fermentation ability and the ethanol tolerance of sake yeast.The genes underexpressed in K-9 more than in X2180-1A were CUP1-1 and CUP1-2, PHO genes, which may explain the low copper tolerance and low acid phosphatase activity of sake yeast. These underexpressed genes agree with the features and the alteration of the genome structure of sake yeast.     

Threonine deaminase from Escherichia coli: feedback-hypersensitive enzyme from a genetic regulatory mutant.

A mutation, ilvA538, in the gene coding for the biosynthetic L-threonine deaminase of Escherichia coli K-12 has previously been demonstrated to have pleiotropic regulatory effects leading to low and invariant expression of some of the isoleucine-valine biosynthetic enzyme, and altered expression of the branched-chain aminoacyl-tRNA synthetases. Strain PS187, which carries the ilvA538 allele, has a partial growth requirement for L-isoleucine and is characterized by a sensitivity to growth inhibition by L-leucine. The experiments reported here demonstrate that the L-threonine deaminase produced by strain PS187 is hypersensitive to inhibition by the pathway end product L-isoleucine. In addition, L-leucine, which acts at relatively high concentrations in vitro as an inhibitor of L-threonine deaminase from the wild type, is a more potent inhibitor of the activity of the mutant enzyme. Forty-six derivatives of strain PS187 were isolated as spontaneous mutants resistant to the growth-inhibitory effects of L-leucine. Two of these, strains MSR14 and MSR16, produce an L-threonine deaminase that is more resistant than the wild type to L-isoleucine inhibition, and intermediate between the wild type and strain PS187 with respect to L-leucine inhibition. Strains MSR14 and MSR16 produce L-threonine deaminase and dihydroxyacid dehydrase, the ilvD gene product, at the low levels characteristic of the parent strain. Other L-leucine-resistant derivatives of strain PS187 produce higher levels of the feedback-hypersensitive L-threonine deaminase. Thus, the sensitivity to growth inhibition by L-leucine observed with strain PS187 appears to be related both to the hypersensitivity of L-threonine deaminase to inhibition of catalytic activity and to the low level of ilv gene expression. The results reported here indicated that L-threonine deaminase is structurally altered in strain PS187, and thus provide further support for the proposal that L-threonine deaminase participates as a genetic regulatory element for the expression of the branched-chain amino acid biosynthetic enzymes.