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Orentaite I, Poranen MM, Oksanen HM, Daugelavicius R, Bamford DH. K2 killer toxin-induced physiological changes in the yeast Saccharomyces cerevisiae. FEMS Yeast Res 2016; 16:fow003. [PMID: 26818855 DOI: 10.1093/femsyr/fow003] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/11/2016] [Indexed: 11/14/2022] Open
Abstract
Saccharomyces cerevisiae cells produce killer toxins, such as K1, K2 and K28, that can modulate the growth of other yeasts giving advantage for the killer strains. Here we focused on the physiological changes induced by K2 toxin on a non-toxin-producing yeast strain as well as K1, K2 and K28 killer strains. Potentiometric measurements were adjusted to observe that K2 toxin immediately acts on the sensitive cells leading to membrane permeability. This correlated with reduced respiration activity, lowered intracellular ATP content and decrease in cell viability. However, we did not detect any significant ATP leakage from the cells treated by killer toxin K2. Strains producing heterologous toxins K1 and K28 were less sensitive to K2 than the non-toxin producing one suggesting partial cross-protection between the different killer systems. This phenomenon may be connected to the observed differences in respiratory activities of the killer strains and the non-toxin-producing strain at low pH. This might also have practical consequences in wine industry; both as beneficial ones in controlling contaminating yeasts and non-beneficial ones causing sluggish fermentation.
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Affiliation(s)
- Irma Orentaite
- Department of Biochemistry, Vytautas Magnus University, Vileikos g. 8, Kaunas 44404, Lithuania
| | - Minna M Poranen
- Department of Biosciences, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland
| | - Hanna M Oksanen
- Department of Biosciences, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland Institute of Biotechnology, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland
| | - Rimantas Daugelavicius
- Department of Biochemistry, Vytautas Magnus University, Vileikos g. 8, Kaunas 44404, Lithuania
| | - Dennis H Bamford
- Department of Biosciences, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland Institute of Biotechnology, University of Helsinki, Viikinkaari 9, Helsinki 00014, Finland
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2
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Servienė E, Lukša J, Orentaitė I, Lafontaine DLJ, Urbonavičius J. Screening the budding yeast genome reveals unique factors affecting K2 toxin susceptibility. PLoS One 2012; 7:e50779. [PMID: 23227207 PMCID: PMC3515549 DOI: 10.1371/journal.pone.0050779] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 10/24/2012] [Indexed: 11/18/2022] Open
Abstract
Background Understanding how biotoxins kill cells is of prime importance in biomedicine and the food industry. The budding yeast (S. cerevisiae) killers serve as a convenient model to study the activity of biotoxins consistently supplying with significant insights into the basic mechanisms of virus-host cell interactions and toxin entry into eukaryotic target cells. K1 and K2 toxins are active at the cell wall, leading to the disruption of the plasma membrane and subsequent cell death by ion leakage. K28 toxin is active in the cell nucleus, blocking DNA synthesis and cell cycle progression, thereby triggering apoptosis. Genome-wide screens in the budding yeast S. cerevisiae identified several hundred effectors of K1 and K28 toxins. Surprisingly, no such screen had been performed for K2 toxin, the most frequent killer toxin among industrial budding yeasts. Principal Findings We conducted several concurrent genome-wide screens in S. cerevisiae and identified 332 novel K2 toxin effectors. The effectors involved in K2 resistance and hypersensitivity largely map in distinct cellular pathways, including cell wall and plasma membrane structure/biogenesis and mitochondrial function for K2 resistance, and cell wall stress signaling and ion/pH homeostasis for K2 hypersensitivity. 70% of K2 effectors are different from those involved in K1 or K28 susceptibility. Significance Our work demonstrates that despite the fact that K1 and K2 toxins share some aspects of their killing strategies, they largely rely on different sets of effectors. Since the vast majority of the host factors identified here is exclusively active towards K2, we conclude that cells have acquired a specific K2 toxin effectors set. Our work thus indicates that K1 and K2 have elaborated different biological pathways and provides a first step towards the detailed characterization of K2 mode of action.
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Affiliation(s)
- Elena Servienė
- Laboratory of Genetics, Institute of Botany, Nature Research Centre, Vilnius, Lithuania
- Department of Chemistry and Bioengineering, Vilnius Gediminas Technical University, Vilnius, Lithuania
- * E-mail: (ES); (DLJL)
| | - Juliana Lukša
- Laboratory of Genetics, Institute of Botany, Nature Research Centre, Vilnius, Lithuania
| | - Irma Orentaitė
- Laboratory of Genetics, Institute of Botany, Nature Research Centre, Vilnius, Lithuania
- Department of Biochemistry and Biotechnologies, Vytautas Magnus University, Kaunas, Lithuania
| | - Denis L. J. Lafontaine
- Fonds de la Recherche Scientifique, Université Libre de Bruxelles, Charleroi-Gosselies, Belgium
- Center for Microscopy and Molecular Imaging, Académie Wallonie-Bruxelles, Charleroi-Gosselies, Belgium
- * E-mail: (ES); (DLJL)
| | - Jaunius Urbonavičius
- Center for Microscopy and Molecular Imaging, Académie Wallonie-Bruxelles, Charleroi-Gosselies, Belgium
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3
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Schmitt MJ, Reiter J. Viral induced yeast apoptosis. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2008; 1783:1413-7. [DOI: 10.1016/j.bbamcr.2008.01.017] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2007] [Revised: 01/17/2008] [Accepted: 01/18/2008] [Indexed: 11/17/2022]
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4
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Killer toxin of Pichia anomala NCYC 432; purification, characterization and its exo-β-1,3-glucanase activity. Enzyme Microb Technol 2006. [DOI: 10.1016/j.enzmictec.2005.11.024] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Reiter J, Herker E, Madeo F, Schmitt MJ. Viral killer toxins induce caspase-mediated apoptosis in yeast. ACTA ACUST UNITED AC 2005; 168:353-8. [PMID: 15668299 PMCID: PMC2171720 DOI: 10.1083/jcb.200408071] [Citation(s) in RCA: 120] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
In yeast, apoptotic cell death can be triggered by various factors such as H2O2, cell aging, or acetic acid. Yeast caspase (Yca1p) and cellular reactive oxygen species (ROS) are key regulators of this process. Here, we show that moderate doses of three virally encoded killer toxins (K1, K28, and zygocin) induce an apoptotic yeast cell response, although all three toxins differ significantly in their primary killing mechanisms. In contrast, high toxin concentrations prevent the occurrence of an apoptotic cell response and rather cause necrotic, toxin-specific cell killing. Studies with Δyca1 and Δgsh1 deletion mutants indicate that ROS accumulation as well as the presence of yeast caspase 1 is needed for apoptosis in toxin-treated yeast cells. We conclude that in the natural environment of toxin-secreting killer yeasts, where toxin concentration is usually low, induction of apoptosis might play an important role in efficient toxin-mediated cell killing.
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Affiliation(s)
- Jochen Reiter
- Applied Molecular Biology, University of the Saarland, D-66041 Saarbrücken, Germany
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6
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Acidophilic structure and killing mechanism of the Pichia farinosa killer toxin SMKT. ACTA ACUST UNITED AC 2004. [DOI: 10.1007/b101843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
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7
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Use of ATP measurements by bioluminescence to quantify yeast’s sensitivity against a killer toxin. Anal Chim Acta 2003. [DOI: 10.1016/j.aca.2003.08.023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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8
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Ahmed A, Sesti F, Ilan N, Shih TM, Sturley SL, Goldstein SA. A molecular target for viral killer toxin: TOK1 potassium channels. Cell 1999; 99:283-91. [PMID: 10555144 DOI: 10.1016/s0092-8674(00)81659-1] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Killer strains of S. cerevisiae harbor double-stranded RNA viruses and secrete protein toxins that kill virus-free cells. The K1 killer toxin acts on sensitive yeast cells to perturb potassium homeostasis and cause cell death. Here, the toxin is shown to activate the plasma membrane potassium channel of S. cerevisiae, TOK1. Genetic deletion of TOK1 confers toxin resistance; overexpression increases susceptibility. Cells expressing TOK1 exhibit toxin-induced potassium flux; those without the gene do not. K1 toxin acts in the absence of other viral or yeast products: toxin synthesized from a cDNA increases open probability of single TOK1 channels (via reversible destabilization of closed states) whether channels are studied in yeast cells or X. laevis oocytes.
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Affiliation(s)
- A Ahmed
- Department of Pediatrics, Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut 06536, USA
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9
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Abstract
Fungal viruses or mycoviruses are widespread in fungi and are believed to be of ancient origin. They have evolved in concert with their hosts and are usually associated with symptomless infections. Mycoviruses are transmitted intracellularly during cell division, sporogenesis and cell fusion, and they lack an extracellular phase to their life cycles. Their natural host ranges are limited to individuals within the same or closely related vegetative compatibility groups. Typically, fungal viruses are isometric particles 25-50 nm in diameter, and possess dsRNA genomes. The best characterized of these belong to the family Totiviridae whose members have simple undivided dsRNA genomes comprised of a coat protein (CP) gene and an RNA dependent RNA polymerase (RDRP) gene. A recently characterized totivirus infecting a filamentous fungus was found to be more closely related to protozoan totiviruses than to yeast totiviruses suggesting these viruses existed prior to the divergence of fungi and protozoa. Although the dsRNA viruses at large are polyphyletic, based on RDRP sequence comparisons, the totiviruses are monophyletic. The theory of a cellular self-replicating mRNA as the origin of totiviruses is attractive because of their apparent ancient origin, the close relationships among their RDRPs, genome simplicity and the ability to use host proteins efficiently. Mycoviruses with bipartite genomes (partitiviruses), like the totiviruses, have simple genomes, but the CP and RDRP genes are on separate dsRNA segments. Because of RDRP sequence similarity, the partitiviruses are probably derived from a totivirus ancestor. The mycoviruses with unencapsidated dsRNA-like genomes (hypoviruses) and those with bacilliform (+) strand RNA genomes (barnaviruses) have more complex genomes and appear to have common ancestry with plant (+) strand RNA viruses in supergroup 1 with potyvirus and sobemovirus lineages, respectively. The La France isometric virus (LIV), an unclassified virus with multipartite dsRNA genome, is associated with a severe die-back disease of the cultivated mushroom. LIV appears to be of recent origin since it differs from its host in codon usage.
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Affiliation(s)
- S A Ghabrial
- Department of Plant Pathology, University of Kentucky, Lexington 40546-0091, USA.
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10
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Izgü F, Altınbay D, Yüceliş A. Identification and killer activity of a yeast contaminating starter cultures ofSaccharomyces cerevisiaestrains used in the Turkish baking industry. Food Microbiol 1997. [DOI: 10.1006/fmic.1996.0082] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Hahnenberger KM, Krystal M, Esposito K, Tang W, Kurtz S. Use of microphysiometry for analysis of heterologous ion channels expressed in yeast. Nat Biotechnol 1996; 14:880-3. [PMID: 9631015 DOI: 10.1038/nbt0796-880] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Measurement of extracellular acidification rates by microphysiometry provides a means to analyze the function of ion channels expressed in yeast cells. These measurements depend on the proton pumping action of the H(+)-ATPase, a central component of the yeast plasma membrane. We used microphysiometry to analyze the activity of two ion channels expressed in yeast. In one example, an inwardly rectifying K+ channel, gpIRK1, provides a potassium uptake function when expressed in a potassium transporter-defective yeast strain. Rates of acidification in gpIRK1-expressing cells directly reflect channel function. Addition of cesium, an inhibitor of gpIRK1 activity, results in an immediate reduction in acidification rates. In a second example, expression of a nonselective cation channel, the influenza virus M2 protein, is believed to interfere with the maintenance of the electrochemical proton gradient by the H(+)-ATPase. In cells expressing the M2 channel, addition of inhibitors increases the rate of proton extrusion. Moreover, functional differences between two M2 inhibitors, amantadine and BL-1743, are distinguished by the microphysiometer. This application demonstrates the utility of the microphysiometer for functional studies of ion channels; it is adaptable to a screening process for compounds that modulate ion channel activity.
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Affiliation(s)
- K M Hahnenberger
- Bristol-Myers Squibb Pharmaceutical Research Institute, Seattle, WA 98121, USA
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13
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Affiliation(s)
- R B Wickner
- Section on Genetics of Simple Eukaryotes, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892-0830, USA.
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14
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Vondrejs V, Janderová B, Valásek L. Yeast killer toxin K1 and its exploitation in genetic manipulations. Folia Microbiol (Praha) 1996; 41:379-93. [PMID: 9131795 DOI: 10.1007/bf02815687] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- V Vondrejs
- Department of Genetics and Microbiology, Faculty of Natural Science, Charles University, Prague, Czech Republic
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15
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Kurtz S, Luo G, Hahnenberger KM, Brooks C, Gecha O, Ingalls K, Numata K, Krystal M. Growth impairment resulting from expression of influenza virus M2 protein in Saccharomyces cerevisiae: identification of a novel inhibitor of influenza virus. Antimicrob Agents Chemother 1995; 39:2204-9. [PMID: 8619568 PMCID: PMC162915 DOI: 10.1128/aac.39.10.2204] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The gene encoding M2, the ion channel-forming protein of influenza virus A, was expressed under the control of an inducible promoter in Saccharomyces cerevisiae. By using single and multicopy plasmids containing GAL promoter-M2 fusions, a correlation was observed between plasmid copy number and growth in medium inducing M2 expression. Cells expressing M2 from multicopy plasmids have reduced growth rates, suggesting that high levels of M2 are toxic to growth. The addition of amantadine, a compound known to block the ion channel activity of certain M2 alleles, restores the growth rates to wild-type levels in cells expressing an amantadine-susceptible allele of M2 but not an amantadine-resistant allele of M2, suggesting that M2 expression in S. cerevisiae results in the formation of functional M2 ion channels. Measurements of extracellular acidification by microphysiometry suggest that proton efflux in M2-expressing cells is altered and that the addition of amantadine permits the reestablishment of the proton gradient. The growth impairment phenotype resulting from M2 expression was used to develop a high-capacity screening assay which identified a novel inhibitor possessing an antiviral profile similar to that of amantadine.
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Affiliation(s)
- S Kurtz
- Department of Microbial Molecular Biology, Bristol-Myers Squibb Pharmaceutical Research Institute, Princeton, New Jersey 08543, USA
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16
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Gu F, Khimani A, Rane SG, Flurkey WH, Bozarth RF, Smith TJ. Structure and function of a virally encoded fungal toxin from Ustilago maydis: a fungal and mammalian Ca2+ channel inhibitor. Structure 1995; 3:805-14. [PMID: 7582897 DOI: 10.1016/s0969-2126(01)00215-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND The P4 strain of the corn smut fungus, Ustilago maydis, secretes a fungal toxin, KP4, encoded by a fungal virus (UMV4) that persistently infects its cells. UMV4, unlike most other (non-fungal) viruses, does not spread to uninfected cells by release into the extracellular milieu during its normal life cycle and is thus dependent upon host survival for replication. In symbiosis with the host fungus, UMV4 encodes KP4 to kill other competitive strains of U. maydis, thereby promoting both host and virus survival. KP4 belongs to a family of fungal toxins and determining its structure should lead to a better understanding of the function and evolutionary origins of these toxins. Elucidation of the mechanism of toxin action could lead to new anti-fungal agents against human pathogens. RESULTS We have determined the atomic structure of KP4 to 1.9 A resolution. KP4 belongs to the alpha/beta-sandwich family, and has a unique topology comprising a five-stranded antiparallel beta-sheet with two antiparallel alpha-helices lying at approximately 45 degrees to these strands. The structure has two left-handed beta alpha beta cross-overs and a basic protuberance extending from the beta-sheet. In vivo experiments demonstrated abrogation of toxin killing by Ca2+ and, to a lesser extent, Mg2+. These results led to experiments demonstrating that the toxin specifically inhibits voltage-gated Ca2+ channels in mammalian cells. CONCLUSIONS Similarities, although somewhat limited, between KP4 and scorpion toxins led us to investigate the possibility that the toxic effects of KP4 may be mediated by inhibition of cation channels. Our results suggest that certain properties of fungal Ca2+ channels are homologous to those in mammalian cells. KP4 may, therefore, be a new tool for studying mammalian Ca2+ channels and current mammalian Ca2+ channel inhibitors may be useful lead compounds for new anti-fungal agents.
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Affiliation(s)
- F Gu
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
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17
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Schmitt MJ. Cloning and expression of a cDNA copy of the viral K28 killer toxin gene in yeast. MOLECULAR & GENERAL GENETICS : MGG 1995; 246:236-46. [PMID: 7862095 DOI: 10.1007/bf00294687] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The killer toxin K28, secreted by certain killer strains of the yeast Saccharomyces cerevisiae is genetically encoded by a 1.9 kb double-stranded RNA, M-dsRNA (M28), that is present within the cell as a cytoplasmically inherited virus-like particle (VLP). For stable maintenance and replication, M28-VLPs depend on a second dsRNA virus (LA), which has been shown to encode the major capsid protein (cap) and a capsid-polymerase fusion protein (cap-pol) that provides the toxin-coding M-satellites with their transcription and replicase functions. K28 toxin-coding M28-VLPs were isolated, purified and used in vitro for the synthesis of the single-stranded M28 transcript, which was shown to be of plus strand polarity and to bind to oligo(dT)-cellulose, indicating that M28(+)ssRNA contains an internal A-rich tract. Strand separation of the 1.9 kb M28-dsRNA and direct RNA sequencing of its 3' ends was performed in order to obtain specific DNA oligonucleotides that could be used as primers for cDNA synthesis. The nucleotide sequence of the toxin-coding M28-cDNA identified a single open reading frame (ORF) coding for a polypeptide of 345 amino acids, which contained two potential Kex2p/Kex1p processing sites and three potential sites for protein N-glycosylation. The toxin-coding cDNA was cloned and expressed in sensitive non-killer strains under the control of the yeast PGK promoter. Upon transformation, this construct conferred the complete K28 phenotype, demonstrating that both toxin and immunity determinants are contained within the cloned cDNA. In vitro translational analysis of the M28(+)ssRNA in vitro transcript identified the primary gene product of M28 as a K28 preprotoxin of 38 kDa (M-p38).
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MESH Headings
- Amino Acid Sequence
- Base Sequence
- Cloning, Molecular
- DNA, Complementary/genetics
- DNA-Directed RNA Polymerases/genetics
- DNA-Directed RNA Polymerases/metabolism
- Gene Expression
- Killer Factors, Yeast
- Molecular Sequence Data
- Mycotoxins/biosynthesis
- Mycotoxins/genetics
- Nucleic Acid Conformation
- Open Reading Frames
- Protein Biosynthesis
- Protein Precursors/genetics
- RNA, Double-Stranded/genetics
- RNA, Double-Stranded/isolation & purification
- RNA, Fungal/genetics
- RNA, Fungal/isolation & purification
- RNA, Viral/genetics
- RNA, Viral/isolation & purification
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae/virology
- Saccharomyces cerevisiae Proteins
- Sequence Analysis, DNA
- Sequence Analysis, RNA
- Transcription, Genetic
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Affiliation(s)
- M J Schmitt
- Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, Germany
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18
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Gu F, Sullivan TS, Che Z, Ganesa C, Flurkey WH, Bozarth RF, Smith TJ. The characterization and crystallization of a virally encoded Ustilago maydis KP4 toxin. J Mol Biol 1994; 243:792-5. [PMID: 7966296 DOI: 10.1016/0022-2836(94)90048-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
KP4 is a virally encoded and highly specific toxin that kills fungi closely related to the fungus Ustilago maydis. The toxin was purified and crystals were formed using ammonium sulfate as precipitant. The crystals belong to the space group P6(1)(5)22 and diffracted to approximately 2.2 A resolution. Circular dicroism spectroscopy suggests that the protein is predominantly comprised of beta-strands.
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Affiliation(s)
- F Gu
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907
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19
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Kurzweilová H, Sigler K. Kinetic studies of killer toxin K1 binding to yeast cells indicate two receptor populations. Arch Microbiol 1994; 162:211-4. [PMID: 7979876 DOI: 10.1007/bf00314477] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
A recently described new method for determination of killer toxin activity was used for kinetic measurements of K1 toxin binding. The cells of the killer sensitive strain Saccharomyces cerevisiae S6 were shown to carry two classes of toxin binding sites differing widely in their half-saturation constants and maximum binding rates. The low-affinity and high-velocity binding component (KT1 = 2.6 x 10(9) L.U./ml, Vmax1 = 0.19 s-1) probably reflects diffusion-limited binding to cell wall receptors; the high-affinity and low-velocity component (KT2 = 3.2 x 10(7) L.U./ml, Vmax2 = 0.03 s-1) presumably indicates the binding of the toxin to plasma membrane receptors. Adsorption of most of the killer toxin K1 to the surface of sensitive cells occurred within 1 min and was virtually complete within 5 min. The amount of toxin that saturated practically all cell receptors was about 600 lethal units (L.U.) per cell of S. cerevisiae S6.
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Affiliation(s)
- H Kurzweilová
- Institute of Microbiology, Czech Academy of Sciences, Prague
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20
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Abstract
Although viruses are widely distributed in fungi, their biological significance to their hosts is still poorly understood. A large number of fungal viruses are associated with latent infections of their hosts. With the exception of the killer-immune character in the yeasts, smuts, and hypovirulence in the chestnut blight fungus, fungal properties that can specifically be related to virus infection are not well defined. Mycoviruses are not known to have natural vectors; they are transmitted in nature intracellularly by hyphal anastomosis and heterokaryosis, and are disseminated via spores. Because fungi have a potential for plasmogamy and cytoplasmic exchange during extended periods of their life cycles and because they produce many types of propagules (sexual and asexual spores), often in great profusion, mycoviruses have them accessible to highly efficient means for transmission and spread. It is no surprise, therefore, that fungal viruses are not known to have an extracellular phase to their life cycles. Although extracellular transmission of a few fungal viruses have been demonstrated, using fungal protoplasts, the lack of conventional methods for experimental transmission of these viruses have been, and remains, an obstacle to understanding their biology. The recent application of molecular biological approaches to the study of mycoviral dsRNAs and the improvements in DNA-mediated fungal transformation systems, have allowed a clearer understanding of the molecular biology of mycoviruses to emerge. Considerable progress has been made in elucidating the genome organization and expression strategies of the yeast L-A virus and the unencapsidated RNA virus associated with hypovirulence in the chestnut blight fungus. These recent advances in the biochemical and molecular characterization of the genomes of fungal viruses and associated satellite dsRNAs, as they relate to the biological properties of these viruses and to their interactions with their hosts are the focus of this chapter.
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Affiliation(s)
- S A Ghabrial
- Department of Plant Pathology, University of Kentucky, Lexington 40546
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21
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Kirsch DR. Development of improved cell-based assays and screens in Saccharomyces through the combination of molecular and classical genetics. Curr Opin Biotechnol 1993; 4:543-52. [PMID: 7764204 DOI: 10.1016/0958-1669(93)90075-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Traditionally, the discovery of pharmaceutical and agrochemical products has largely depended on mass screening. Over the years, screen design and screening programs have evolved in terms of the sensitivity with which active material can be identified, the number of samples that can be tested, and the types of molecular targets and cellular functions that can be conveniently assayed. More recently, screens with desirable properties have been developed for a great variety of molecular targets through the exploitation of Saccharomyces molecular biology and genetics. Recent advances have enabled researchers to develop yeast-based screens for agents acting on a number of new therapeutic targets: G-protein linked receptors, cytoplasmic receptors, ion (potassium) channels, novel fungal cell wall enzymes, fungal sterol biosynthesis enzymes, antiviral targets, immunosuppressive targets, cyclic nucleotide phosphodiesterase, oncogenes and the multiple drug resistance (MDR) protein.
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Affiliation(s)
- D R Kirsch
- American Cynamid, Molecular Genetic Screen Design, Princeton, New Jersey 08543-0400
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22
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Evidence that the SKI antiviral system of Saccharomyces cerevisiae acts by blocking expression of viral mRNA. Mol Cell Biol 1993. [PMID: 8321235 DOI: 10.1128/mcb.13.7.4331] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The SKI2 gene is part of a host system that represses the copy number of the L-A double-stranded RNA (dsRNA) virus and its satellites M and X dsRNA, of the L-BC dsRNA virus, and of the single-stranded replicon 20S RNA. We show that SKI2 encodes a 145-kDa protein with motifs characteristic of helicases and nucleolar proteins and is essential only in cells carrying M dsRNA. Unexpectedly, Ski2p does not repress M1 dsRNA copy number when M1 is supported by aN L-A cDNA clone; nonetheless, it did lower the levels of M1 dsRNA-encoded toxin produced. Since toxin secretion from cDNA clones of M1 is unaffected by Ski2p, these data suggest that Ski2p acts by specifically blocking translation of viral mRNAs, perhaps recognizing the absence of cap or poly(A). In support of this idea, we find that Ski2p represses production of beta-galactosidase from RNA polymerase I [no cap and no poly(A)] transcripts but not from RNA polymerase II (capped) transcripts.
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Widner WR, Wickner RB. Evidence that the SKI antiviral system of Saccharomyces cerevisiae acts by blocking expression of viral mRNA. Mol Cell Biol 1993; 13:4331-41. [PMID: 8321235 PMCID: PMC359991 DOI: 10.1128/mcb.13.7.4331-4341.1993] [Citation(s) in RCA: 60] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The SKI2 gene is part of a host system that represses the copy number of the L-A double-stranded RNA (dsRNA) virus and its satellites M and X dsRNA, of the L-BC dsRNA virus, and of the single-stranded replicon 20S RNA. We show that SKI2 encodes a 145-kDa protein with motifs characteristic of helicases and nucleolar proteins and is essential only in cells carrying M dsRNA. Unexpectedly, Ski2p does not repress M1 dsRNA copy number when M1 is supported by aN L-A cDNA clone; nonetheless, it did lower the levels of M1 dsRNA-encoded toxin produced. Since toxin secretion from cDNA clones of M1 is unaffected by Ski2p, these data suggest that Ski2p acts by specifically blocking translation of viral mRNAs, perhaps recognizing the absence of cap or poly(A). In support of this idea, we find that Ski2p represses production of beta-galactosidase from RNA polymerase I [no cap and no poly(A)] transcripts but not from RNA polymerase II (capped) transcripts.
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Affiliation(s)
- W R Widner
- Section on Genetics of Simple Eukaryotes, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892
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24
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Tao J, Ginzberg I, Koltin Y, Bruenn JA. Mutants of Ustilago maydis defective in production of one of two polypeptides of KP6 toxin from the preprotoxin. MOLECULAR & GENERAL GENETICS : MGG 1993; 238:234-40. [PMID: 8479428 DOI: 10.1007/bf00279552] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Double-stranded RNA viruses of Ustilago maydis encode secreted killer toxins to which other cells of the same species and closely related species are sensitive. KP6 toxin consists of two polypeptides, alpha and beta, produced from a single precursor preprotoxin. In this work, we cloned complementary DNA for the toxin-encoding segment of two of the KP6 nonkiller mutants NK3 and NK13 that secrete the beta and alpha polypeptides, respectively. Both sequence analysis of the cDNA clones and in vitro translation of the toxin-encoding double-stranded RNAs showed that both mutants can produce full-length preprotoxins. Cys51 in alpha is converted to Arg in NK3 and Thr25 and Lys42 in beta are changed to Pro and Arg, respectively, in NK13. Although alpha and beta are encoded in a single prepropolypeptide, only the beta polypeptide is secreted by NK3 and only the alpha polypeptide is secreted by NK13. This differential expression of peptides from one precursor is a unique phenomenon. Neither of the nonsecreted polypeptides accumulated in the cytosol. The possible effects of these mutations on preprotoxin folding and their consequences for toxin secretion are discussed.
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Affiliation(s)
- J Tao
- Department of Biological Sciences, SUNY, Buffalo 14260
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25
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Finkler A, Peery T, Tao J, Bruenn J, Koltin I. Immunity and resistance to the KP6 toxin of Ustilago maydis. MOLECULAR & GENERAL GENETICS : MGG 1992; 233:395-403. [PMID: 1620096 DOI: 10.1007/bf00265436] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The KP6 toxin of Ustilago maydis, encoded by segmented double-stranded (ds) RNA viruses, is lethal to sensitive strains of the same species and related species. The toxin consists of two polypeptides, alpha and beta, synthesized as a single preprotoxin, which are not covalently linked. Neither polypeptide alone is toxic, but killer activity can be restored by in vitro and in vivo complementation. Killer-secreting strains are resistant to the toxin they produce. Resistance is conferred by a single recessive nuclear gene. This study describes a search for cytoplasmic factors that may confer resistance, also referred to as immunity. The approaches used to detect cytoplasmic immunity included transmission of dsRNA and transmission of virus particles to sensitive cells by cytoduction, cytoplasmic mixing in diploids and infection with viruses. An alternative approach was also used to express cloned cDNAs of the KP6 toxin-encoding dsRNA and of the alpha and beta polypeptides. The results indicated that no immunity to KP6 can be detected. While KP6, alpha and beta polypeptides were expressed by resistant cells, neither KP6 nor beta were expressed in sensitive strains. The alpha polypeptide was expressed in sensitive cells, but it did not confer immunity. These results suggest that neither the preprotoxin nor the alpha or beta polypeptides confer immunity and thus beta may be the toxic component of the binary toxin.
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Affiliation(s)
- A Finkler
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Israel
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26
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Schmitt MJ, Tipper DJ. Genetic analysis of maintenance and expression of L and M double-stranded RNAs from yeast killer virus K28. Yeast 1992; 8:373-84. [PMID: 1626429 DOI: 10.1002/yea.320080505] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The killer phenotype expressed by Saccharomyces cerevisiae strain 28 differs from that of the more extensively studied K1 and K2 killers with respect to immunity, mode of toxin action and cell wall primary toxin receptor. We previously demonstrated that the M28 and L28 dsRNAs found in strain 28 are present in virus-like particles (VLPs) and that transfection with these VLPs is sufficient to confer the complete K28 phenotype on a dsRNA-free recipient cell. We also demonstrated that L28, like the L-A-H species in K1 killers, has [HOK] activity required for maintenance of M1-dsRNA, and predicted that M28 would share with M1 dependence on L-A for replication. We now confirm this prediction by genetic and biochemical analysis of the effects of representative mak, ski and mkt mutations on M28 maintenance, demonstrating that M28 replication resembles M1 in all respects. We also show that L28 is an L-A-H species lacking [B] activity, and that M28 excludes both M1 and M2 from the same cytoplasm. Stable coexpression of K28 phenotype from M28 and of K1 phenotype from an M1-cDNA clone was demonstrated. Exclusion, therefore, acts at the level of dsRNA replication, presumably reflecting competition for the L-A-H encoded capsid and cap-pol fusion protein, rather than reflecting incompatibility of toxin or immunity expression. Finally, we show that expression of active K28 toxin, but not of K28 immunity, requires the Kex2 endoprotease.
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Affiliation(s)
- M J Schmitt
- Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, Germany
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27
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Abstract
The cytoplasmic L-A dsRNA virus of Saccharomyces cerevisiae consists of a 4.5 kb dsRNA and the two gene products it encodes; the capsid (cap) and at least one copy of the capsid-polymerase (cap-pol) fusion protein. Virion cap-pol catalyses transcription of the plus (sense)-strand; this is extruded from the virus and serves as messenger for synthesis of cap and cap-pol. Nascent cap-pol binds to a specific domain in the plus strand to initiate encapsidation and then catalyses minus-strand synthesis to complete the replication cycle. Products of at least three host genes are required for replication, and virus copy number is kept at tolerable levels by the SKI antivirus system. S. cerevisiae killer viruses are satellite dsRNAs that use a similar encapsidation domain to parasitize the L-A replication machinery. They encode precursors of secreted polypeptide toxins and immunity (specific resistance) determinants and are self-selecting. Three unique killer types, K1, K2 and K28, are currently recognized. They are distinguished by an absence of cross-immunity and by toxin properties and lethal mechanisms; while K1 and K2 toxins bind to cell-wall glucan and disrupt membrane functions, K28 toxin binds to mannoprotein and causes inhibition of DNA synthesis.
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Affiliation(s)
- D J Tipper
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655
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28
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Abstract
K1 killer toxin is a secreted, pore-forming protein that kills sensitive yeast cells. The heterodimeric toxin is processed from a precursor in the Golgi, and has allowed identification of the KEX2- and KEX1-encoded proteases. The toxin binds to a glucan receptor on the cell wall of target yeast, and mutational analysis implicates both the alpha- and beta-toxin subunits in receptor binding. Toxin-resistant mutants with altered cell-wall glucans have helped to outline a pathway of assembly of these polysaccharides. Patch-clamp technology has demonstrated the nature of the lethal channel in toxin-treated plasma membranes. The hydrophobic alpha-subunit-encoding region is the site of all mutations affecting channel formation. Immunity to the toxin is conferred by the toxin precursor, and immunity mutations map to the region encoding the alpha subunit. The precursor probably competes with the toxin to prevent channel formation in toxin-producing cells, but the basis of this remains unknown. This toxin/immunity system has a domain structure that differs from that of other characterized toxins and has no known homologues.
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Affiliation(s)
- H Bussey
- Department of Biology, McGill University, Montreal, Quebec, Canada
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29
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Abstract
To determine the functional domains of K1 killer toxin, we analyzed the phenotypes of a set of mutations throughout regions encoding the alpha- and beta-toxin subunits that allow secretion of mutant toxins. A range of techniques have been used to examine the ability of mutant toxins to bind to beta-glucan cell wall receptor and to form lethal ion channels. Our results indicate that both the alpha and beta subunits are involved in beta-glucan receptor binding. Defects in ion channel formation and toxin immunity are confined to the hydrophobic alpha subunit of the toxin.
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30
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Abstract
To determine the functional domains of K1 killer toxin, we analyzed the phenotypes of a set of mutations throughout regions encoding the alpha- and beta-toxin subunits that allow secretion of mutant toxins. A range of techniques have been used to examine the ability of mutant toxins to bind to beta-glucan cell wall receptor and to form lethal ion channels. Our results indicate that both the alpha and beta subunits are involved in beta-glucan receptor binding. Defects in ion channel formation and toxin immunity are confined to the hydrophobic alpha subunit of the toxin.
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Affiliation(s)
- H Zhu
- Department of Biology, McGill University, Montreal, Quebec, Canada
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31
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Polonelli L, Conti S, Gerloni M, Magliani W, Chezzi C, Morace G. Interfaces of the yeast killer phenomenon. Crit Rev Microbiol 1991; 18:47-87. [PMID: 1854433 DOI: 10.3109/10408419109113509] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A new prophylactic and therapeutic antimicrobial strategy based on a specific physiological target that is effectively used by killer yeasts in their natural ecological competition is theorized. The natural system exploited is the yeast killer phenomenon previously adopted as an epidemiological marker for intraspecific differentiation of opportunistic yeasts, hyphomycetes, and bacteria. Pathogenic microorganisms (Candida albicans) may be susceptible to the activity of yeast killer toxins due to the presence of specific cell wall receptors. On the basis of the idiotypic network, we report that antiidiotypic antibodies, produced against a monoclonal antibody bearing the receptor-like idiotype, are in vivo protecting animals immunized through idiotypic vaccination and in vitro mimicking the antimicrobial activity of yeast killer toxins, thus acting as antibiotics.
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Affiliation(s)
- L Polonelli
- Institute of Microbiology, University of Parma, Italy
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32
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Martinac B, Zhu H, Kubalski A, Zhou XL, Culbertson M, Bussey H, Kung C. Yeast K1 killer toxin forms ion channels in sensitive yeast spheroplasts and in artificial liposomes. Proc Natl Acad Sci U S A 1990; 87:6228-32. [PMID: 1696721 PMCID: PMC54506 DOI: 10.1073/pnas.87.16.6228] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The patch-clamp technique was used to examine the plasma membranes of sensitive yeast spheroplasts exposed to partially purified killer toxin preparations. Asolectin liposomes in which the toxin was incorporated were also examined. Excised inside-out patches from these preparations often revealed at 118 pS conductance appearing in pairs. The current through this conductance flickered rapidly among three states: dwelling mostly at the unit-open state, less frequently at the two-unit-open state, and more rarely at the closed state. Membrane voltages from -80 to 80 mV had little influence on the opening probability. The current reversed near the equilibrium potential of K+ in asymmetric KCl solutions and also reversed near O mV at symmetric NaCl vs. KCl solutions. The two levels of the conductance were likely due to the toxin protein, as treatment of spheroplasts or liposomes with extracellular protein preparations from isogenic yeasts deleted for the toxin gene gave no such conductance levels. These results show that in vivo the killer-toxin fraction can form a cation channel that seldom closes regardless of membrane voltage. We suggest that this channel causes the death of sensitive yeast cells.
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Affiliation(s)
- B Martinac
- Laboratory of Molecular Biology, University of Wisconsin-Madison 53706
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33
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Conclusion. Cell Mol Life Sci 1990. [DOI: 10.1007/bf02027314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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