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Papkou A, Garcia-Pastor L, Escudero JA, Wagner A. A rugged yet easily navigable fitness landscape. Science 2023; 382:eadh3860. [PMID: 37995212 DOI: 10.1126/science.adh3860] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Accepted: 09/29/2023] [Indexed: 11/25/2023]
Abstract
Fitness landscape theory predicts that rugged landscapes with multiple peaks impair Darwinian evolution, but experimental evidence is limited. In this study, we used genome editing to map the fitness of >260,000 genotypes of the key metabolic enzyme dihydrofolate reductase in the presence of the antibiotic trimethoprim, which targets this enzyme. The resulting landscape is highly rugged and harbors 514 fitness peaks. However, its highest peaks are accessible to evolving populations via abundant fitness-increasing paths. Different peaks share large basins of attraction that render the outcome of adaptive evolution highly contingent on chance events. Our work shows that ruggedness need not be an obstacle to Darwinian evolution but can reduce its predictability. If true in general, the complexity of optimization problems on realistic landscapes may require reappraisal.
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Affiliation(s)
- Andrei Papkou
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - Lucia Garcia-Pastor
- Departamento de Sanidad Animal and VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain
| | - José Antonio Escudero
- Departamento de Sanidad Animal and VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain
| | - Andreas Wagner
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
- Swiss Institute of Bioinformatics, Lausanne, Switzerland
- The Santa Fe Institute, Santa Fe, NM, USA
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2
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Folate Biosynthesis, Reduction, and Polyglutamylation and the Interconversion of Folate Derivatives. EcoSal Plus 2015; 2. [PMID: 26443588 DOI: 10.1128/ecosalplus.3.6.3.6] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Many microorganisms and plants possess the ability to synthesize folic acid derivatives de novo, initially forming dihydrofolate. All the folic acid derivatives that serve as recipients and donors of one-carbon units are derivatives of tetrahydrofolate, which is formed from dihydrofolate by an NADPH-dependent reduction catalyzed by dihydrofolate reductase (FolA). This review discusses the biosynthesis of dihydrofolate monoglutamate, its reduction to tetrahydrofolate monoglutamate, and the addition of glutamyl residues to form folylpolyglutamates. Escherichia coli and Salmonella, like many microorganisms that can synthesize folate de novo, appear to lack the ability to transport folate into the cell and are thus highly susceptible to inhibitors of folate biosynthesis. The review includes a brief discussion of the inhibition of folate biosynthesis by sulfa drugs. The folate biosynthetic pathway can be divided into two sections. First, the aromatic precursor chorismate is converted to paminobenzoic acid (PABA) by the action of three proteins. Second, the pteridine portion of folate is made from GTP and coupled to PABA to generate dihydropteroate, and the bifunctional protein specified by folC, dihydrofolate synthetase, or folylpolyglutamate synthetase, adds the initial glutamate molecule to form dihydrofolate (H2PteGlu1, or dihydropteroylmonoglutamate). Bacteriophage T4 infection of E. coli has been shown to cause alterations in the metabolism of folate derivatives. Infection is associated with an increase in the chain lengths in folylpolyglutamates and particularly the accumulation of hexaglutamate derivatives.
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Tan C, Guo L, Ai Y, Li J, Wang L, Sancar A, Luo Y, Zhong D. Direct determination of resonance energy transfer in photolyase: structural alignment for the functional state. J Phys Chem A 2014; 118:10522-30. [PMID: 25000823 PMCID: PMC4234433 DOI: 10.1021/jp504349b] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Photoantenna is essential to energy
transduction in photoinduced
biological machinery. A photoenzyme, photolyase, has a light-harvesting
pigment of methenyltetrahydrofolate (MTHF) that transfers its excitation
energy to the catalytic flavin cofactor FADH¯ to enhance DNA-repair
efficiency. Here we report our systematic characterization and direct
determination of the ultrafast dynamics of resonance energy transfer
from excited MTHF to three flavin redox states in E. coli photolyase by capturing the intermediates formed through the energy
transfer and thus excluding the electron-transfer quenching pathway.
We observed 170 ps for excitation energy transferring to the fully
reduced hydroquinone FADH¯, 20 ps to the fully oxidized FAD,
and 18 ps to the neutral semiquinone FADH•, and
the corresponding orientation factors (κ2) were determined
to be 2.84, 1.53 and 1.26, respectively, perfectly matching with our
calculated theoretical values. Thus, under physiological conditions
and over the course of evolution, photolyase has adopted the optimized
orientation of its photopigment to efficiently convert solar energy
for repair of damaged DNA.
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Affiliation(s)
- Chuang Tan
- Department of Physics, Department of Chemistry and Biochemistry, and Programs of Biophysics, Chemical Physics, and Biochemistry, The Ohio State University , 191 West Woodruff Avenue, Columbus, Ohio 43210, United States
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Chopra S, Dooling RM, Horner CG, Howell EE. A balancing act between net uptake of water during dihydrofolate binding and net release of water upon NADPH binding in R67 dihydrofolate reductase. J Biol Chem 2007; 283:4690-8. [PMID: 18086667 DOI: 10.1074/jbc.m709443200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
R67 dihydrofolate reductase (DHFR) catalyzes the reduction of dihydrofolate (DHF) to tetrahydrofolate using NADPH as a cofactor. This enzyme is a homotetramer possessing 222 symmetry, and a single active site pore traverses the length of the protein. A promiscuous binding surface can accommodate either DHF or NADPH, thus two nonproductive complexes can form (2NADPH or 2DHF) as well as a productive complex (NADPH.DHF). The role of water in binding was monitored using a number of different osmolytes. From isothermal titration calorimetry (ITC) studies, binding of NADPH is accompanied by the net release of 38 water molecules. In contrast, from both steady state kinetics and ITC studies, binding of DHF is accompanied by the net uptake of water. Although different osmolytes have similar effects on NADPH binding, variable results are observed when DHF binding is probed. Sensitivity to water activity can also be probed by an in vivo selection using the antibacterial drug, trimethoprim, where the water content of the media is decreased by increasing concentrations of sorbitol. The ability of wild type and mutant clones of R67 DHFR to allow host Escherichia coli to grow in the presence of trimethoprim plus added sorbitol parallels the catalytic efficiency of the DHFR clones, indicating water content strongly correlates with the in vivo function of R67 DHFR.
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Affiliation(s)
- Shaileja Chopra
- Department of Biochemistry, Cellular, and Molecular Biology, University of Tennessee, Knoxville, Tennessee 37996-0840, USA
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5
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Wilquet V, Van de Casteele M, Gigot D, Legrain C, Glansdorff N. Dihydropteridine reductase as an alternative to dihydrofolate reductase for synthesis of tetrahydrofolate in Thermus thermophilus. J Bacteriol 2004; 186:351-5. [PMID: 14702303 PMCID: PMC305743 DOI: 10.1128/jb.186.2.351-355.2004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
A strategy devised to isolate a gene coding for a dihydrofolate reductase from Thermus thermophilus DNA delivered only clones harboring instead a gene (the T. thermophilus dehydrogenase [DH(Tt)] gene) coding for a dihydropteridine reductase which displays considerable dihydrofolate reductase activity (about 20% of the activity detected with 6,7-dimethyl-7,8-dihydropterine in the quinonoid form as a substrate). DH(Tt) appears to account for the synthesis of tetrahydrofolate in this bacterium, since a classical dihydrofolate reductase gene could not be found in the recently determined genome nucleotide sequence (A. Henne, personal communication). The derived amino acid sequence displays most of the highly conserved cofactor and active-site residues present in enzymes of the short-chain dehydrogenase/reductase family. The enzyme has no pteridine-independent oxidoreductase activity, in contrast to Escherichia coli dihydropteridine reductase, and thus appears more similar to mammalian dihydropteridine reductases, which do not contain a flavin prosthetic group. We suggest that bifunctional dihydropteridine reductases may be responsible for the synthesis of tetrahydrofolate in other bacteria, as well as archaea, that have been reported to lack a classical dihydrofolate reductase but for which possible substitutes have not yet been identified.
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Affiliation(s)
- Valérie Wilquet
- Microbiology, Université Libre de Bruxelles, B-1070 Brussels, Belgium
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6
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Giladi M, Altman-Price N, Levin I, Levy L, Mevarech M. FolM, a new chromosomally encoded dihydrofolate reductase in Escherichia coli. J Bacteriol 2003; 185:7015-8. [PMID: 14617668 PMCID: PMC262705 DOI: 10.1128/jb.185.23.7015-7018.2003] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2003] [Accepted: 09/02/2003] [Indexed: 11/20/2022] Open
Abstract
Escherichia coli (thyA DeltafolA) mutants are viable and can grow in minimal medium when supplemented with thymidine alone. Here we present evidence from in vivo and in vitro studies that the ydgB gene determines an alternative dihydrofolate reductase that is related to the trypanosomatid pteridine reductases. We propose to rename this gene folM.
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Affiliation(s)
- Moshe Giladi
- Department of Molecular Microbiology and Biotechnology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel
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7
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Sancar A. Structure and function of DNA photolyase and cryptochrome blue-light photoreceptors. Chem Rev 2003; 103:2203-37. [PMID: 12797829 DOI: 10.1021/cr0204348] [Citation(s) in RCA: 939] [Impact Index Per Article: 44.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Aziz Sancar
- Department of Biochemistry and Biophysics, Mary Ellen Jones Building, CB 7260, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27599, USA.
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8
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Abstract
Reduced folate derivatives participate in numerous reactions of bacterial intermediary metabolism. Consequently, the well-characterized enzyme implicated in the formation of tetrahydrofolate--dihydrofolate reductase FolA--was considered to be essential for bacterial growth. However, comparative genomics has revealed several bacterial genome sequences that appear to lack the folA gene. Here, we provide in silico evidence indicating that folA-lacking bacteria use a recently discovered class of flavin-dependent thymidylate synthases for deoxythymidine-5'-monophosphate synthesis, and propose that many bacteria must contain uncharacterized sources for reduced folate molecules that are still waiting to be discovered.
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Affiliation(s)
- Hannu Myllykallio
- Institut de Génétique et Microbiologie CNRS UMR8621, Université de Paris-Sud, Orsay, France.
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9
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Chirwa NT, Herrington MB. CsgD, a regulator of curli and cellulose synthesis, also regulates serine hydroxymethyltransferase synthesis in Escherichia coli K-12. MICROBIOLOGY (READING, ENGLAND) 2003; 149:525-535. [PMID: 12624214 DOI: 10.1099/mic.0.25841-0] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The homologous CsgD and AgfD proteins are members of the FixJ/UhpA/LuxR family and are proposed to regulate curli (thin aggregative fibres) and cellulose production by Escherichia coli and Salmonella enterica serovar Typhimurium, respectively. A plasmid containing part of the csgD gene was isolated during a screen for multicopy suppressors of glycine auxotrophy caused by deleting the folA gene in E. coli. The sequence of the plasmid suggests it encodes a chimaeric protein. Plasmids containing the intact csgD or agfD gene also caused suppression. Cells transformed with the recombinant plasmids contained higher serine hydroxymethyltransferase (SHMT) activity than controls. The increase could also be monitored by assaying beta-galactosidase activity from a reporter strain with part of the SHMT gene, glyA, fused to lacZ. The increase in SHMT activity was sufficient to correct the glycine auxotrophy of strains lacking folA. The recombinant plasmids also enabled K-12 strains that are not curli-proficient to make curli. Curlin, the major component of curli, contains more glycine than normal E. coli proteins. It is proposed that CsgD upregulates glyA to facilitate synthesis of curli. It is suggested that recombinant plasmids produce enough CsgD or chimaeric protein to titrate out a ligand that switches CsgD into its inactive form. As a result, sufficient active CsgD is present to activate genes in its regulon. It is concluded that CsgD increases expression of the glyA gene either directly or indirectly.
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Affiliation(s)
- Neema T Chirwa
- Biology Department, Concordia University, 1455 Maisonneuve Boulevard West, Montreal, Quebec, Canada H3G 1M8
| | - Muriel B Herrington
- Biology Department, Concordia University, 1455 Maisonneuve Boulevard West, Montreal, Quebec, Canada H3G 1M8
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10
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Herrington MB, Chirwa NT. Growth properties of afolAnull mutant ofEscherichia coliK12. Can J Microbiol 1999. [DOI: 10.1139/w98-229] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In Escherichia coli, dihydrofolate reductase is required for both the de novo synthesis of tetrahydrofolate and the recycling of dihydrofolate produced during the synthesis of thymidylate. The coding region of the dihydrofolate reductase gene, folA, was replaced with a kanamycin resistance determinant. Unlike earlier deletions, this mutation did not disrupt flanking genes. When the mutation was transferred into a wild-type strain and a thymidine- (thy) requiring strain, the resulting strains were viable but slow growing on rich medium. Both synthesized less folate than their parents, as judged by the incorporation of radioactive para-aminobenzoic acid. The derivative of the wild-type strain did not grow on any defined minimal media tested. In contrast, the derivative of the thy-requiring strain grew slowly on minimal medium with thy but exhibited auxotrophies on some combinations of supplements. These results suggest that when folates are limited, they can be distributed appropriately to folate-dependent biosynthetic reactions only under some conditions. Key words: dihydrofolate reductase, Escherichia coli, biosynthesis, folates, one-carbon metabolism.
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11
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Huang EY, Mohler AM, Rohlman CE. Protein expression in response to folate stress in Escherichia coli. J Bacteriol 1997; 179:5648-53. [PMID: 9287033 PMCID: PMC179449 DOI: 10.1128/jb.179.17.5648-5653.1997] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Interruption of folate metabolism by trimethoprim results in the elevated expression of folate stress proteins in Escherichia coli. E. coli grown in culture medium supplemented with the folate-dependent metabolites glycine, methionine, and the purine nucleoside inosine shows reduced expression of folate stress proteins. The folate stress proteins include the universal stress protein, the ferric uptake regulatory repressor, and possibly, lipoamide dehydrogenase, the L protein component of the glycine cleavage enzyme complex.
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Affiliation(s)
- E Y Huang
- Department of Chemistry, Pomona College, Claremont, California 91711, USA
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12
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Papadopoulou B, Roy G, Mourad W, Leblanc E, Ouellette M. Changes in folate and pterin metabolism after disruption of the Leishmania H locus short chain dehydrogenase gene. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37285-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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13
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Kim ST, Sancar A. Photochemistry, photophysics, and mechanism of pyrimidine dimer repair by DNA photolyase. Photochem Photobiol 1993; 57:895-904. [PMID: 8337263 DOI: 10.1111/j.1751-1097.1993.tb09232.x] [Citation(s) in RCA: 121] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
DNA photolyases photorepair pyrimidine dimers (Pyr < > Pyr) in DNA as well as RNA and thus reverse the harmful effects of UV-A (320-400 nm) and UV-B (280-320 nm) radiations. Photolyases from various organisms have been found to contain two noncovalently bound cofactors; one is a fully reduced flavin adenine dinucleotide (FADH-) and the other, commonly known as second chromophore, is either methenyltetrahydrofolate (MTHF) or 8-hydroxydeazaflavin (8-HDF). The second chromophore in photolyase is a light-harvesting molecule that absorbs mostly in the near-UV and visible wavelengths (300-500 nm) with its high extinction coefficient. The second chromophore then transfers its excitation energy to the FADH-. Subsequently, the photoexcited FADH- transfers an electron to the Pyr < > Pyr generating a dimer radical anion (Pyr < > Pyr.-) and a neutral flavin radical (FADH.). The Pyr < > Pyr.- is very unstable and undergoes spontaneous splitting followed by a back electron transfer to the FADH.. In addition to the main catalytic cofactor FADH-, a Trp (Trp277 in Escherichia coli) in apophotolyase, independent of other chromophores, also functions as a sensitizer to repair Pyr < > Pyr by direct electron transfer.
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Affiliation(s)
- S T Kim
- Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599-7260
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14
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Basso J, Tiganos E, Herrington MB. Nonsense suppression in thymine-requiring strains of Escherichia coli is a consequence of altered folate metabolism. MOLECULAR & GENERAL GENETICS : MGG 1993; 238:218-24. [PMID: 8479427 DOI: 10.1007/bf00279550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Thymine-requiring strains of Escherichia coli suppress nonsense and frameshift mutants of T4 phage. We proposed that these mutants make errors during translation because of an imbalance in folate metabolism. A thymine-requiring strain grown under suppressing conditions has elevated levels of reduced folates. We tested the effect of either mutational blocks or the inhibition of various steps in folate biosynthesis on suppression. Conditions which prevent the accumulation of 5-methyl tetrahydrofolate inhibit suppression, suggesting that elevated levels of this folate are required for suppression. Furthermore, conditions that result in an accumulation in dihydrofolate inhibit suppression.
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Affiliation(s)
- J Basso
- Biology Department, Concordia University, Montreal, Quebec, Canada
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15
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Krishnan BR, Berg DE. Viability of folA-null derivatives of wild-type (thyA+) Escherichia coli K-12. J Bacteriol 1993; 175:909-11. [PMID: 8423162 PMCID: PMC196245 DOI: 10.1128/jb.175.3.909-911.1993] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Dihydrofolate reductase (the folA gene product) catalyzes the synthesis of tetrahydrofolate, a key methyl donor in many biosynthetic pathways. Loss of folA had been thought to be lethal to wild-type (thyA+) Escherichia coli. Viable folA-null derivatives of thyA+ E. coli were obtained, however, by recombining a folA deletion linked to a Kanr selectable marker into a lambda folA+ phage and using this phage to transduce cells to kanamycin resistance. folA-null strains were slow growing, formed small colonies, and were auxotrophic for thymidine, adenine, methionine, glycine, and pantothenate.
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Affiliation(s)
- B R Krishnan
- Department of Molecular Microbiology, Washington University Medical School, St. Louis, Missouri 63110
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Huang T, Barclay BJ, Kalman TI, von Borstel RC, Hastings PJ. The phenotype of a dihydrofolate reductase mutant of Saccharomyces cerevisiae. Gene 1992; 121:167-71. [PMID: 1427091 DOI: 10.1016/0378-1119(92)90177-q] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We have constructed a dihydrofolate reductase mutant (dfr1) of Saccharomyces cerevisiae. The mutant has auxotrophic growth requirements for the C1 metabolites dTMP, adenine, histidine and methionine, similar to those of wild-type (wt) strains grown in the presence of methotrexate (MTX). However, unlike wt strains treated with MTX, the growth requirements of the dfr1 mutant are not satisfied by exogenous 5-formyltetrahydrofolic acid (FA; folinic acid) in complex (YEPD) medium. This result is surprising, as yeast cells treated with MTX are expected to be phenocopies of dfr1 mutants. The inability of the mutants to metabolize FA suggests that the DFR1 gene product may have a role in folate metabolism in addition to its well-characterized function in the reduction of dihydrofolate. From dfr1 strains, we have isolated secondary mutants whose growth can be supported by FA in YEPD medium. This FA-utilizing phenotype is attributable to recessive mutations which we have designated fou. In addition to their inability to metabolize FA, the dfr1 strains are unable to grow on medium containing the non-fermentable carbon source glycerol, suggesting that the DFR1 gene product is also required for mitochondrial function. In order to overcome this lack of respiratory activity in the dfr1 mutants, we isolated strains containing a dominant mutation, DIR, which allows growth on glycerol in the presence of antifolate drugs. When crossed into dfr1 strains, the DIR mutation conferred respiratory competence. These strains should be useful in a variety of studies on the genetics and biochemistry of folate metabolism in this simple eukaryote.
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Affiliation(s)
- T Huang
- Department of Genetics, University of Alberta, Edmonton, Canada
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Azakami H, Sugino H, Murooka Y. Cloning and nucleotide sequence of a negative regulator gene for Klebsiella aerogenes arylsulfatase synthesis and identification of the gene as folA. J Bacteriol 1992; 174:2344-51. [PMID: 1551851 PMCID: PMC205857 DOI: 10.1128/jb.174.7.2344-2351.1992] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
A negative regulator gene for synthesis of arylsulfatase in Klebsiella aerogenes was cloned. Deletion analysis showed that the regulator gene was located within a 1.6-kb cloned segment. Transfer of the plasmid, which contains the cloned fragment, into constitutive atsR mutant strains of K. aerogenes resulted in complementation of atsR; the synthesis of arylsulfatase was repressed in the presence of inorganic sulfate or cysteine, and this repression was relieved, in each case, by the addition of tyramine. The nucleotide sequence of the 1.6-kb fragment was determined. From the amino acid sequence deduced from the DNA sequence, we found two open reading frames. One of them lacked the N-terminal region but was highly homologous to the gene which codes for diadenosine tetraphosphatase (apaH) in Escherichia coli. The other open reading frame was located counterclockwise to the apaH-like gene. This gene was highly homologous to the gene which codes for dihydrofolate reductase (folA) in E. coli. We detected 30 times more activity of dihydrofolate reductase in the K. aerogenes strains carrying the plasmid, which contains the arylsulfatase regulator gene, than in the strains without plasmid. Further deletion analysis showed that the K. aerogenes folA gene is consistent with the essential region required for the repression of arylsulfatase synthesis. Transfer of a plasmid containing the E. coli folA gene into atsR mutant cells of K. aerogenes resulted in repression of the arylsulfatase synthesis. Thus, we conclude that the folA gene codes a negative regulator for the ats operon.
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Affiliation(s)
- H Azakami
- Department of Fermentation Technology, Faculty of Engineering, Hiroshima University, Japan
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18
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Ouellette M, Borst P. Drug resistance and P-glycoprotein gene amplification in the protozoan parasite Leishmania. Res Microbiol 1991; 142:737-46. [PMID: 1961984 DOI: 10.1016/0923-2508(91)90089-s] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Amplification of the H circle is often associated with methotrexate (MTX) selection in Leishmania species. We have shown that the H circle of Leishmania tarentolae contains an open reading frame, ItpgpA, that has the attributes of P-glycoproteins (large plasma membrane proteins known to extrude lipophilic drugs from mammalian cells). H region amplification was also noted in some mutants selected for resistance to arsenite and vinblastine. Mutants having the complete 68-kb circles were cross-resistant to MTX, but two arsenite mutants having only part of the H region amplified, but including ItpgpA, were not cross-resistant to MTX. These results suggest that the putative determinant for MTX resistance present on the H circle is not ItpgpA. We have also determined how ItpgpA-containing plasmids were generated from the chromosomal copy. The H circle contains a 30-kb inverted duplication separated by two unique DNA segments. The corresponding H region of chromosomal DNA has only one copy of the duplicated DNA. We have shown that the two unique segments in chromosomal DNA are flanked by inverted repeats suggesting that H circles could be formed by a foldback mechanism (see fig. 2). Unexpectedly, a plasmid present in cells selected for arsenite resistance lacked part of the H region and the long inverted repeats. It appears to have been formed by intrachromosomal recombination between two P-glycoprotein genes, ItpgpA and ItpgpB, located adjacent to the H region. Our results show that under drug pressure, the same P-glycoprotein-encoding region in Leishmania may be amplified by very different mechanisms and yield different amplicons.
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Affiliation(s)
- M Ouellette
- Service d'Infectiologie, CHUL, Québec, Canada
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