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Wilken SE, Seppälä S, Lankiewicz TS, Saxena M, Henske JK, Salamov AA, Grigoriev IV, O’Malley MA. Genomic and proteomic biases inform metabolic engineering strategies for anaerobic fungi. Metab Eng Commun 2020; 10:e00107. [PMID: 31799118 PMCID: PMC6883316 DOI: 10.1016/j.mec.2019.e00107] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2019] [Revised: 10/24/2019] [Accepted: 11/04/2019] [Indexed: 12/22/2022] Open
Abstract
Anaerobic fungi (Neocallimastigomycota) are emerging non-model hosts for biotechnology due to their wealth of biomass-degrading enzymes, yet tools to engineer these fungi have not yet been established. Here, we show that the anaerobic gut fungi have the most GC depleted genomes among 443 sequenced organisms in the fungal kingdom, which has ramifications for heterologous expression of genes as well as for emerging CRISPR-based genome engineering approaches. Comparative genomic analyses suggest that anaerobic fungi may contain cellular machinery to aid in sexual reproduction, yet a complete mating pathway was not identified. Predicted proteomes of the anaerobic fungi also contain an unusually large fraction of proteins with homopolymeric amino acid runs consisting of five or more identical consecutive amino acids. In particular, threonine runs are especially enriched in anaerobic fungal carbohydrate active enzymes (CAZymes) and this, together with a high abundance of predicted N-glycosylation motifs, suggests that gut fungal CAZymes are heavily glycosylated, which may impact heterologous production of these biotechnologically useful enzymes. Finally, we present a codon optimization strategy to aid in the development of genetic engineering tools tailored to these early-branching anaerobic fungi.
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Affiliation(s)
- St. Elmo Wilken
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - Susanna Seppälä
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - Thomas S. Lankiewicz
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
- Department of Evolution Ecology and Marine Biology, University of California, Santa Barbara, CA, 93106, USA
| | - Mohan Saxena
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - John K. Henske
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
| | - Asaf A. Salamov
- US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA
| | - Igor V. Grigoriev
- US Department of Energy Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA, 94598, USA
| | - Michelle A. O’Malley
- Department of Chemical Engineering, University of California, Santa Barbara, CA, 93106, USA
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Pérez-Sánchez L, González E, Colón-Lorenzo EE, González-Velázquez W, González-Méndez R, Rodríguez-del Valle N. Interaction of the heterotrimeric G protein alpha subunit SSG-1 of Sporothrix schenckii with proteins related to stress response and fungal pathogenicity using a yeast two-hybrid assay. BMC Microbiol 2010; 10:317. [PMID: 21143936 PMCID: PMC3018405 DOI: 10.1186/1471-2180-10-317] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 12/09/2010] [Indexed: 11/15/2022] Open
Abstract
Background Important biological processes require selective and orderly protein-protein interactions at every level of the signalling cascades. G proteins are a family of heterotrimeric GTPases that effect eukaryotic signal transduction through the coupling of cell surface receptors to cytoplasmic effector proteins. They have been associated with growth and pathogenicity in many fungi through gene knock-out studies. In Sporothrix schenckii, a pathogenic, dimorphic fungus, we previously identified a pertussis sensitive G alpha subunit, SSG-1. In this work we inquire into its interactions with other proteins. Results Using the yeast two-hybrid technique, we identified protein-protein interactions between SSG-1 and other important cellular proteins. The interactions were corroborated using co-immuneprecipitation. Using these techniques we identified a Fe/Mn superoxide dismutase (SOD), a glyceraldehyde-3-P dehydrogenase (GAPDH) and two ion transport proteins, a siderophore-iron transporter belonging to the Major Facilitator Superfamily (MFS) and a divalent-cation transporter of the Nramp (natural resistance-associated macrophage protein) family as interacting with SSG-1. The cDNA's encoding these proteins were sequenced and bioinformatic macromolecular sequence analyses were used for the correct classification and functional assignment. Conclusions This study constitutes the first report of the interaction of a fungal G alpha inhibitory subunit with SOD, GAPDH, and two metal ion transporters. The identification of such important proteins as partners of a G alpha subunit in this fungus suggests possible mechanisms through which this G protein can affect pathogenicity and survival under conditions of environmental stress or inside the human host. The two ion transporters identified in this work are the first to be reported in S. schenckii and the first time they are identified as interacting with fungal G protein alpha subunits. The association of G protein alpha subunits to transport molecules reinforces the role of G proteins in the response to environmental signals and also highlights the involvement of fungal G protein alpha subunits in nutrient sensing in S. schenckii. These interactions suggest that these permeases could function as transceptors for G proteins in fungi.
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Affiliation(s)
- Lizaida Pérez-Sánchez
- Department of Microbiology and Medical Zoology, Medical Sciences Campus, University of Puerto Rico, PO Box 365067, San Juan, PR 00936-5067, USA
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Heterotrimeric G-protein subunit function in Candida albicans: both the alpha and beta subunits of the pheromone response G protein are required for mating. EUKARYOTIC CELL 2008; 7:1591-9. [PMID: 18658257 DOI: 10.1128/ec.00077-08] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A pheromone-mediated signaling pathway that couples seven-transmembrane-domain (7-TMD) receptors to a mitogen-activated protein kinase module controls Candida albicans mating. 7-TMD receptors are typically connected to heterotrimeric G proteins whose activation regulates downstream effectors. Two Galpha subunits in C. albicans have been identified previously, both of which have been implicated in aspects of pheromone response. Cag1p was found to complement the mating pathway function of the pheromone receptor-coupled Galpha subunit in Saccharomyces cerevisiae, and Gpa2p was shown to have a role in the regulation of cyclic AMP signaling in C. albicans and to repress pheromone-mediated arrest. Here, we show that the disruption of CAG1 prevented mating, inactivated pheromone-mediated arrest and morphological changes, and blocked pheromone-mediated gene expression changes in opaque cells of C. albicans and that the overproduction of CAG1 suppressed the hyperactive cell cycle arrest exhibited by sst2 mutant cells. Because the disruption of the STE4 homolog constituting the only C. albicans gene for a heterotrimeric Gbeta subunit also blocked mating and pheromone response, it appears that in this fungal pathogen the Galpha and Gbeta subunits do not act antagonistically but, instead, are both required for the transmission of the mating signal.
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Lockhart SR, Zhao R, Daniels KJ, Soll DR. Alpha-pheromone-induced "shmooing" and gene regulation require white-opaque switching during Candida albicans mating. EUKARYOTIC CELL 2004; 2:847-55. [PMID: 14555467 PMCID: PMC219372 DOI: 10.1128/ec.2.5.847-855.2003] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
A 14-mer alpha-pheromone peptide of Candida albicans was chemically synthesized and used to analyze the role of white-opaque switching in the mating process. The alpha-pheromone peptide blocked cell multiplication and induced "shmooing" in a/a cells expressing the opaque-phase phenotype but not in a/a cells expressing the white-phase phenotype. The alpha-pheromone peptide induced these effects at 25 degrees C but not at 37 degrees C. An analysis of mating-associated gene expression revealed several categories of gene regulation, including (i) MTL-homozygous-specific, pheromone stimulated, switching-independent (CAG1 and STE4); (ii) mating type-specific, pheromone-induced, switching-independent (STE2); and (iii) pheromone-induced, switching-dependent (FIG1, KAR4, and HWP1). An analysis of switching-regulated genes revealed an additional category of opaque-phase-specific genes that are downregulated by alpha-pheromone only in a/a cells (OP4, SAP1, and SAP3). These results demonstrate that alpha-pheromone causes shmooing, the initial step in the mating process, only in a/a cells expressing the opaque phenotype and only at temperatures below that in the human host. These results further demonstrate that although some mating-associated genes are stimulated by the alpha-pheromone peptide in both white- and opaque-phase cells, others are stimulated only in opaque-phase cells, revealing a category of gene regulation unique to C. albicans in which alpha-pheromone induction requires the white-opaque transition. These results demonstrate that in C. albicans, the mating process and associated gene regulation must be examined within the context of white-opaque switching.
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Affiliation(s)
- Shawn R Lockhart
- Department of Biological Sciences, University of Iowa, Iowa City, Iowa 52242-1324, USA
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Pendrak ML, Yan SS, Roberts DD. Hemoglobin regulates expression of an activator of mating-type locus alpha genes in Candida albicans. EUKARYOTIC CELL 2004; 3:764-75. [PMID: 15189997 PMCID: PMC420132 DOI: 10.1128/ec.3.3.764-775.2004] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2003] [Accepted: 03/24/2004] [Indexed: 11/20/2022]
Abstract
Phenotypic switching from the white to the opaque phase is a necessary step for mating in the pathogenic fungus Candida albicans. Suppressing switching during vascular dissemination of the organism may be advantageous, because opaque cells are more susceptible to host defenses. A repressor of white-opaque switching, HBR1 (hemoglobin response gene 1), was identified based on its specific induction following growth in the presence of exogenous hemoglobin. Deletion of a single HBR1 allele allowed opaque phase switching and mating competence, accompanied by a lack of detectable MTL alpha1 and alpha2 gene expression and enhanced MTLa1 gene expression. Conversely, overexpression of Hbr1p or exposure to hemoglobin increased MTLalpha gene expression. The a1/alpha2 repressed target gene CAG1 was derepressed in the same mutant in a hemoglobin-sensitive manner. Regulation of CAG1 by hemoglobin required an intact MTLa1 gene. Several additional Mtlp targets were perturbed in HBR1 mutants in a manner consistent with commitment to an a mating phenotype, including YEL007w, MFalpha, HST6, and RAM2. Therefore, Hbr1 is part of a host factor-regulated signaling pathway that controls white-opaque switching and mating in the absence of allelic deletion at the MTL locus.
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Affiliation(s)
- Michael L Pendrak
- Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1500, USA.
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Sánchez-Martínez C, Pérez-Martín J. Gpa2, a G-protein alpha subunit required for hyphal development in Candida albicans. EUKARYOTIC CELL 2002; 1:865-74. [PMID: 12477787 PMCID: PMC138749 DOI: 10.1128/ec.1.6.865-874.2002] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Candida albicans is able to respond to environmental changes by inducing a distinct morphological program, which is related to the ability to infect mammalian hosts. Although some of the signal transduction pathways involved in this response are known, it is not clear how the environmental signals are sensed and transmitted to these transduction cascades. In this work, we have studied the function of GPA2, a new gene from C. albicans, which encodes a G-protein alpha-subunit homologue. We demonstrate that Gpa2 plays an important role in the yeast-hypha dimorphic transition in the response of C. albicans to some environmental inducers. Deletion of both alleles of the GPA2 gene causes in vitro defects in morphological transitions in Spider medium and SLAD medium and in embedded conditions but not in medium containing serum. These defects cannot be reversed by exogenous addition of cyclic AMP. However, overexpression of HST7, which encodes a component of the filament-inducing mitogen-activated protein kinase (MAPK) cascade, bypasses the Gpa2 requirement. We have obtained different gain-of-function and loss-of-function mutant alleles of the GPA2 gene, which we have introduced in several C. albicans genetic backgrounds. Our results indicate that, in response to environmental cues, Gpa2 is required for the regulation of a MAPK signaling pathway.
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Affiliation(s)
- Cristina Sánchez-Martínez
- Department of Microbial Biotechnology, Centro Nacional de Biotecnología CSIC, Campus de Cantoblanco-UAM, 28049 Madrid, Spain
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Fowler TJ, DeSimone SM, Mitton MF, Kurjan J, Raper CA. Multiple sex pheromones and receptors of a mushroom-producing fungus elicit mating in yeast. Mol Biol Cell 1999; 10:2559-72. [PMID: 10436012 PMCID: PMC25488 DOI: 10.1091/mbc.10.8.2559] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/1999] [Accepted: 05/27/1999] [Indexed: 11/11/2022] Open
Abstract
The mushroom-producing fungus Schizophyllum commune has thousands of mating types defined, in part, by numerous lipopeptide pheromones and their G protein-linked receptors. Compatible combinations of pheromones and receptors encoded by different mating types regulate a pathway of sexual development leading to mushroom formation and meiosis. A complex set of pheromone-receptor interactions maximizes the likelihood of outbreeding; for example, a single pheromone can activate more than one receptor and a single receptor can be activated by more than one pheromone. The current study demonstrates that the sex pheromones and receptors of Schizophyllum, when expressed in Saccharomyces cerevisiae, can substitute for endogenous pheromone and receptor and induce the yeast pheromone response pathway through the yeast G protein. Secretion of active Schizophyllum pheromone requires some, but not all, of the biosynthetic machinery used by the yeast lipopeptide pheromone a-factor. The specificity of interaction among pheromone-receptor pairs in Schizophyllum was reproduced in yeast, thus providing a powerful system for exploring molecular aspects of pheromone-receptor interactions for a class of seven-transmembrane-domain receptors common to a wide range of organisms.
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Affiliation(s)
- T J Fowler
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, Vermont 05405, USA
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Kallal L, Kurjan J. Analysis of the receptor binding domain of Gpa1p, the G(alpha) subunit involved in the yeast pheromone response pathway. Mol Cell Biol 1997; 17:2897-907. [PMID: 9111362 PMCID: PMC232142 DOI: 10.1128/mcb.17.5.2897] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Saccharomyces cerevisiae G protein alpha subunit Gpa1p is involved in the response of both MATa and MAT alpha cells to pheromone. We mutagenized the GPA1 C terminus to characterize the receptor-interacting domain and to investigate the specificity of the interactions with the a- and alpha-factor receptors. The results are discussed with respect to a structural model of the Gpa1p C terminus that was based on the crystal structure of bovine transducin. Some mutants showed phenotypes different than the pheromone response and mating defects expected for mutations that affect receptor interactions, and therefore the mutations may affect other aspects of Gpa1p function. Most of the mutations that resulted in pheromone response and mating defects had similar effects in MATa and MAT alpha cells, suggesting that they affect the interactions with both receptors. Overexpression of the pheromone receptors increased the mating of some of the mutants tested but not the wild-type strain, consistent with defects in mutant Gpa1p-receptor interactions. The regions identified by the mating-defective mutants correlated well with the regions of mammalian G(alpha) subunits implicated in receptor interactions. The strongest mating type-specific effects were seen for mutations to proline and a mutation of a glycine residue predicted to form a C-terminal beta turn. The analogous beta turn in mammalian G(alpha) subunits undergoes a conformational change upon receptor interaction. We propose that the conformation of this region of Gpa1p differs during the interactions with the a- and alpha-factor receptors and that these mating type-specific mutations preclude the orientation necessary for interaction with one of the two receptors.
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Affiliation(s)
- L Kallal
- Department of Microbiology and Molecular Genetics, University of Vermont, Burlington 05405, USA
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9
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Gao S, Nuss DL. Distinct roles for two G protein alpha subunits in fungal virulence, morphology, and reproduction revealed by targeted gene disruption. Proc Natl Acad Sci U S A 1996; 93:14122-7. [PMID: 11038529 PMCID: PMC19504 DOI: 10.1073/pnas.93.24.14122] [Citation(s) in RCA: 161] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Reduced accumulation of the GTP-binding protein G(i)alpha subunit CPG-1, due either to hypovirus infection or transgenic cosuppression, correlates with virulence attenuation of the chestnut blight fungus, Cryphonectria parasitica. The role of G protein-mediated signal transduction in fungal virulence was further examined by targeted disruption of the gene cpg-1, encoding CPG-1, and a second Galpha gene, cpg-2, encoding the subunit CPG-2. Disruption of cpg-1 resulted in a set of phenotypic changes similar to, but more severe than, those associated with hypovirus infection. Changes included a marked reduction in fungal growth rate and loss of virulence, asexual sporulation, female fertility, and transcriptional induction of the gene lac-1, encoding the enzyme laccase. In contrast, cpg-2 disruption resulted in only slight reductions in growth rate and asexual sporulation and no significant reduction in virulence, female fertility, or lac-1 mRNA inducibility. These results provide definitive confirmation of previous correlative evidence that suggested a requirement of CPG-1-linked signaling for a number of fungal processes, including virulence and reproduction, while demonstrating that a second Galpha, CPG-2, is dispensable for these processes. They also significantly strengthen support for the apparent linkage between hypovirus-mediated disruption of G protein signal transduction and attenuation of fungal virulence.
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Affiliation(s)
- S Gao
- Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, University of Maryland, College Park, MD 20742-3351, USA
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10
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Clark KL, Feldmann PJ, Dignard D, Larocque R, Brown AJ, Lee MG, Thomas DY, Whiteway M. Constitutive activation of the Saccharomyces cerevisiae mating response pathway by a MAP kinase kinase from Candida albicans. MOLECULAR & GENERAL GENETICS : MGG 1995; 249:609-21. [PMID: 8544826 DOI: 10.1007/bf00418030] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The HST7 gene of Candida albicans encodes a protein with structural similarity to MAP kinase kinases. Expression of this gene in Saccharomyces cerevisiae complements disruption of the Ste7 MAP kinase kinase required for both mating in haploid cells and pseudohyphal growth in diploids. However, Hst7 expression does not complement loss of either the Pbs2 (Hog4) MAP kinase kinase required for response to high osmolarity, or loss of the Mkk1 and Mkk2 MAP kinase kinases required for proper cell wall biosynthesis. Intriguingly, HST7 acts as a hyperactive allele of STE7; expression of Hst7 activates the mating pathway even in the absence of upstream signaling components including the Ste7 regulator Ste11, elevates the basal level of the pheromone-inducible FUS1 gene, and amplifies the pseudohyphal growth response in diploid cells. Thus Hst7 appears to be at least partially independent of upstream activators or regulators, but selective in its activity on downstream target MAP kinases. Creation of Hst7/Ste7 hybrid proteins revealed that the C-terminal two-thirds of Hst7, which contains the protein kinase domain, is sufficient to confer this partial independence of upstream activators.
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Affiliation(s)
- K L Clark
- Eukaryotic Genetics Group, Biotechnology Research Institute, National Research Council Canada, Montreal, Quebec, Canada
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11
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Rustchenko EP, Howard DH, Sherman F. Chromosomal alterations of Candida albicans are associated with the gain and loss of assimilating functions. J Bacteriol 1994; 176:3231-41. [PMID: 8195078 PMCID: PMC205493 DOI: 10.1128/jb.176.11.3231-3241.1994] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
We have demonstrated that a normal laboratory strain of Candida albicans spontaneously produces mutants which acquire the ability to assimilate certain carbon sources that are not utilized by the parental strain. The examination of mutants acquiring the ability to utilize either sorbose or D-arabinose revealed a few additional phenotypic changes, including the gain and loss of the capacity to assimilate other carbon sources. The change of assimilation patterns resembled the polymorphic variation of assimilation patterns found among different wild-type strains of C. albicans. Most importantly, these sorbose- and D-arabinose-positive mutants were associated with chromosomal rearrangements, with each class of positive mutants having alterations of specific chromosomes. These findings demonstrated for the first time that chromosomal alterations in C. albicans are involved in genetic variation of fundamental functions of this asexual microorganism.
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Affiliation(s)
- E P Rustchenko
- Department of Biochemistry, University of Rochester School of Medicine and Dentistry, New York 14642
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Anderson J, Srikantha T, Morrow B, Miyasaki SH, White TC, Agabian N, Schmid J, Soll DR. Characterization and partial nucleotide sequence of the DNA fingerprinting probe Ca3 of Candida albicans. J Clin Microbiol 1993; 31:1472-80. [PMID: 8314989 PMCID: PMC265564 DOI: 10.1128/jcm.31.6.1472-1480.1993] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The moderately repetitive Ca3 fragment of Candida albicans has been used as an effective DNA fingerprinting probe in epidemiological studies. EcoRI digestion of Ca3 DNA results in seven fragments of 4.2 kb (A), 2.98 kb (B), 2.85 kb (C), 0.77 kb (D1), 0.77 kb (D2), 0.38 kb (E), and 0.30 kb (F). Five of these EcoRI fragments have been mapped in the 5'-3' order C B D1 A D2. The intact Ca3 probe and the three largest EcoRI fragments, A, B, and C, were individually used to probe Southern blots of EcoRI-digested DNA of a set of test strains, transverse alternating field electrophoresis-separated chromosomes of strain 3153A, and Northern (RNA) blots of test strain 3153A. Fragments, A, B, and C each generate a different Southern blot hybridization pattern with EcoRI-digested whole-cell DNA; Ca3 sequences are present in at least five of seven separable chromosomes and a minichromosome of strain 3153A; fragments A, B, and C are distributed differently on chromosomes; and fragments A, B, and C do not cross-hybridize. Ca3 hybridizes to three major transcripts of 2.8, 2.3, and 1.5 kb. Fragment A hybridizes intensely to the 1.5-kb transcript, while fragments B and C both hybridize intensely to the 2.8- and 2.3-kb transcripts. The B fragment, which contains 2,980 bp and contributes to the major portion of the Ca3 pattern, was sequenced. Both direct and inverted repeat sequence motifs were identified. These results provide us with initial insights into the evolution of the Ca3 pattern and the nature of the probe.
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Affiliation(s)
- J Anderson
- Department of Biology, University of Iowa, Iowa City 52242-1324
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Abstract
We have identified sequences at the telomeres of the yeast Candida albicans and have found that they are composed of tandem copies of a 23-bp sequence. Through the cloning of native telomeric ends and the characterization and cloning of a "healed" end, we demonstrate that these repeated sequences are sufficient to function as a telomere. All copies of the 23-bp repeat that have been sequenced from a number of C. albicans strains are identical. In contrast, adjacent subtelomeric sequences are variable both between strains and within the WO-1 strain. In the WO-1 strain, the lengths of the telomeres are dependent upon growth temperature and are substantially longer at higher temperatures. Telomere growth is accompanied by increases in the number of the 23-bp repeats present on the telomeric fragments. These results suggest that either telomerase-maintained telomeres can be more complex in structure than was previously imagined or that Candida telomeres are maintained via a telomerase-independent mechanism.
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14
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Abstract
We have identified sequences at the telomeres of the yeast Candida albicans and have found that they are composed of tandem copies of a 23-bp sequence. Through the cloning of native telomeric ends and the characterization and cloning of a "healed" end, we demonstrate that these repeated sequences are sufficient to function as a telomere. All copies of the 23-bp repeat that have been sequenced from a number of C. albicans strains are identical. In contrast, adjacent subtelomeric sequences are variable both between strains and within the WO-1 strain. In the WO-1 strain, the lengths of the telomeres are dependent upon growth temperature and are substantially longer at higher temperatures. Telomere growth is accompanied by increases in the number of the 23-bp repeats present on the telomeric fragments. These results suggest that either telomerase-maintained telomeres can be more complex in structure than was previously imagined or that Candida telomeres are maintained via a telomerase-independent mechanism.
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Affiliation(s)
- M J McEachern
- Department of Molecular Biology, Research Institute of Scripps Clinic, La Jolla, California 92037
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Whiteway M, Dignard D, Thomas DY. Dominant negative selection of heterologous genes: isolation of Candida albicans genes that interfere with Saccharomyces cerevisiae mating factor-induced cell cycle arrest. Proc Natl Acad Sci U S A 1992; 89:9410-4. [PMID: 1409649 PMCID: PMC50141 DOI: 10.1073/pnas.89.20.9410] [Citation(s) in RCA: 111] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We have used a genomic library of Candida albicans to transform Saccharomyces cerevisiae and screened for genes that act similarly to dominant negative mutations by interfering with pheromone-mediated cell cycle arrest. Six different plasmids were identified from 2000 transformants; four have been sequenced. One gene (CZF1) encodes a protein with structural motifs characteristic of a transcription factor. A second gene (CCN1) encodes a cyclin homologue, a third (CRL1) encodes a protein with sequence similarity to GTP-binding proteins of the RHO family, and a fourth (CEK1) encodes a putative kinase of the ERK family. Since CEK1 confers a phenotype similar to that of the structurally related S. cerevisiae gene KSS1 but cannot complement a KSS1 defect, it is evident that dominant negative selection can identify proteins that complementation screens would miss. Because dominant negative mutations exert their influence even in wild-type strain backgrounds, this approach should be a general method for the analysis of complex cellular processes in organisms not amenable to direct genetic analysis.
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Affiliation(s)
- M Whiteway
- Eukaryotic Genetics Group, National Research Council of Canada, Montréal, Québec
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