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Metabolic engineering of Corynebacterium glutamicum for 2-ketoisocaproate production. Appl Microbiol Biotechnol 2013; 98:297-311. [DOI: 10.1007/s00253-013-5310-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Revised: 09/30/2013] [Accepted: 10/01/2013] [Indexed: 10/26/2022]
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Molskness TA, Alic M, Gold MH. Characterization of Leucine Auxotrophs of the White Rot Basidiomycete Phanerochaete chrysosporium. Appl Environ Microbiol 2010; 51:1170-3. [PMID: 16347073 PMCID: PMC239040 DOI: 10.1128/aem.51.6.1170-1173.1986] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Six leucine auxotrophic strains of the white rot basidiomycete Phanerochaete chrysosporium were characterized genetically and biochemically. Complementation studies involving the use of heterokaryons identified three leucine complementation groups. Since all of the leucine auxotrophs grew on minimal medium supplemented with alpha-ketoisocaproate as well as with leucine, the transaminase catalyzing the last step in the leucine pathway was apparently normal in all strains. Therefore, the wild-type, auxotrophic, and several heterokaryotic strains were assayed for the activities of the other enzymes specific to leucine biosynthesis. Leu2 and Leu4 strains (complementation group I) lacked only alpha-isopropylmalate synthase activity; Leu3 and Leu6 strains (group III) lacked isopropylmalate isomerase activity; and Leu1 and Leu5 strains (group II) lacked beta-isopropylmalate dehydrogenase. Heterokaryons formed from leucine auxotrophs of different complementation groups had levels of activity for all three enzymes similar to those found in the wild-type strain.
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Affiliation(s)
- T A Molskness
- Department of Chemical, Biological, and Environmental Sciences, Oregon Graduate Center, Beaverton, Oregon 97006-1999
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Kohlhaw GB. Leucine biosynthesis in fungi: entering metabolism through the back door. Microbiol Mol Biol Rev 2003; 67:1-15, table of contents. [PMID: 12626680 PMCID: PMC150519 DOI: 10.1128/mmbr.67.1.1-15.2003] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
After exploring evolutionary aspects of branched-chain amino acid biosynthesis, the review focuses on the extended leucine biosynthetic pathway as it operates in Saccharomyces cerevisiae. First, the genes and enzymes specific for the leucine pathway are considered: LEU4 and LEU9 (encoding the alpha-isopropylmalate synthase isoenzymes), LEU1 (isopropylmalate isomerase), and LEU2 (beta-isopropylmalate dehydrogenase). Emphasis is given to the unusual distribution of the branched-chain amino acid pathway enzymes between mitochondrial matrix and cytosol, on the newly defined role of Leu5p, and on regulatory mechanisms governing gene expression and enzyme activity, including new evidence for the metabolic importance of the regulation of alpha-isopropylmalate synthase by coenzyme A. Next, structure-function relationships of the transcriptional regulator Leu3p are addressed, defining its dual role as activator and repressor and discussing evidence in support of the self-masking model. Recent data pointing at a more extended Leu3p regulon are discussed. An overview of the layered controls of the extended leucine pathway is provided that includes a description of the newly recognized roles of Ilv5p and Bat1p in maintaining mitochondrial integrity. Finally, branched-chain amino acid biosynthesis and its regulation in other fungi are summarized, the question of leucine as metabolic signal is addressed, and possible directions of future research in this area are outlined.
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Affiliation(s)
- Gunter B Kohlhaw
- Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
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Jarai G, Yagmai B, Fu YH, Marzluf GA. Regulation of branched-chain amino acid biosynthesis in Neurospora crassa: cloning and characterization of the leu-1 and ilv-3 genes. MOLECULAR & GENERAL GENETICS : MGG 1990; 224:383-8. [PMID: 1980003 DOI: 10.1007/bf00262432] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The genes coding for the branched-chain amino acid biosynthetic enzymes comprise an integrated regulatory system. The expression of the several structural genes coding for enzymes of the isoleucine-valine and leucine pathways is controlled in parallel by the positive-acting regulatory gene, leu-3. The leu-1 and ilv-3 genes, coding for beta-isopropyl-malate dehydrogenase and aceto-hydroxyacid synthase, respectively, were cloned from a cosmid library. Restriction fragment length polymorphism analysis revealed that the two cloned fragments indeed mapped to the genomic locations of the leu-1 and ilv-3 genes, respectively. Northern blot analysis demonstrated that the leu-1 gene is transcribed to give an mRNA of approximately 1.5 kb, whereas the ilv-3 transcript size is 2.6 kb. The expression of both genes appears to be regulated at the transcriptional level. One leu-3 regulatory mutant was greatly deficient in both leu-1 and ilv-3 mRNAs, whereas another leu-3 allele showed an unusual antiparallel pattern of regulation.
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Affiliation(s)
- G Jarai
- Department of Biochemistry, Ohio State University, Columbus 4321
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Loppes R, Heindricks R. New arginine-requiring mutants in Chlamydomonas reinhardtii. Arch Microbiol 1986. [DOI: 10.1007/bf00412801] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Armaleo D, Fischer M, Gross SR. Effect of alpha-isopropylmalate on the synthesis of RNA and protein in Neurospora. MOLECULAR & GENERAL GENETICS : MGG 1985; 200:346-9. [PMID: 3162080 DOI: 10.1007/bf00425447] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The leu-3/alpha-IPM (alpha-isopropylmalate) regulatory system, previously shown to control several genes of leucine, isoleucine, valine, and histidine biosynthesis, appears likely to be involved also in the regulation of overall RNA and protein synthesis in Neurospora. Upon addition of alpha-IPM the synthesis of all major species of stable RNA was found to be transiently inhibited by approximately 50%. A similar reduction was observed in overall protein synthesis. The inhibition was dependent in both cases on a functional leu-3 gene product, in conformance with previously established patterns of alpha-IPM dependent gene regulation. The overt resemblance of the phenomenon described here to the 'stringent response' of bacteria is noted but neither the mechanism of inhibition nor the precise role of alpha-IPM in the process has been established.
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Kidd GL, Gross SR. Specific regulatory interconnection between the leucine and histidine pathways of Neurospora crassa. J Bacteriol 1984; 158:121-7. [PMID: 6325383 PMCID: PMC215388 DOI: 10.1128/jb.158.1.121-127.1984] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Leucine auxotrophs of Neurospora fall into two discrete categories with respect to sensitivity to the herbicide, 3-amino-1,2,4-triazole. The pattern of resistance corresponds exactly to the ability to produce the leucine pathway control elements, alpha-isopropylmalate and the leu-3 product. An analysis of the regulatory response of the production of enzymes of histidine biosynthesis to alpha-isopropylmalate implicates the control elements of the leucine pathway as important components of the mechanism governing the production of the target enzyme of aminotriazole inhibition, imidazoleglycerol-phosphate dehydratase (EC 4.2.1.19). The evidence suggests that the regulatory interconnection between the two pathways is direct and is independent of other general integrating regulatory mechanisms which appear to be operative in both pathways. A general method for isolating leu-1 and leu-2, as well as other regulatory mutants, is described, which takes advantage of the specificity of the resistance to the inhibitor. Use of analogous systems is prescribed for the analysis of other regulatory interconnections which, like this one, might not be anticipated directly from structural or biosynthetic considerations.
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The Genetics and Physiology of Non-inducibility in Volvox carteri f. nagariensis IYGENGAR. ACTA ACUST UNITED AC 1980. [DOI: 10.1016/s0003-9365(80)80001-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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11
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Reichenbecher VE, Fischer M, Gross SR. Regulation of isopropylmalate isomerase synthesis in Neurospora crassa. J Bacteriol 1978; 133:794-801. [PMID: 146702 PMCID: PMC222090 DOI: 10.1128/jb.133.2.794-801.1978] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The capacity to synthetize isopropylmalate isomerase (EC 4.2.1.33) by Neurospora crassa increased during induction in the presence of cycloheximide but was inhibited by proflavine and other inhibitors of RNA synthesis. Turnover of the enzyme once formed appeared negligible, but the message (measured as enzyme-forming capacity) had a half-life of 4 to 8 min. A comparison of the kinetics of induction in the wild type and a newly isolated alpha-isopropylmalate-permeable strain suggested strongly that feedback control by leucine of alpha-isopropylmalate production can adequately serve as the primary physiological regulator of endogenous inducer concentration. Genetic data are presented which implicate the involvement of two unlinked genes, ipm-1 and ipm-2, in determining permeation of alpha-isopropylmalate.
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Reichenbecher VE, Gross SR. Structural features of normal and complemented forms of the Neurospora isopropylmalate isomerase. J Bacteriol 1978; 133:802-10. [PMID: 146703 PMCID: PMC222091 DOI: 10.1128/jb.133.2.802-810.1978] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The isopropylmalate isomerase (EC 4.2.1.33) of Neurospora crassa is a globular protein consisting of a single polypeptide chain with a molecular weight of about 90,000. The isomerase cannot easily be freed of a contaminating protease which cleaves the enzyme into two major fragments, one of approximately 56,000 and the other 37,000 daltons. This suggests that the folded polypeptide chain may contain some hinge point or loop exposed on the surface which makes it susceptible to proteolytic attack. Most of the isomerase activity extracted from the wild-type strain is in monomer form. However, a small fraction of the activity in crude extracts is found in multimeric aggregates, and the active isomerase extracted from complementing leu-2 heterokaryons consists entirely of dimers and higher multimers. These observations suggest that, though active as a monomer, a significant fraction of the normal enzyme might be organized in multimeric form within the cell.
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Fantes PA, Roberts LM, Huetter R. Free tryptophan pool and tryptophan biosynthetic enzymes in Saccharomyces cerevisiae. Arch Microbiol 1976; 107:207-14. [PMID: 769720 DOI: 10.1007/bf00446842] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The free tryptophan pool and the levels of two enzymes of tryptophan biosynthesis (anthranilate synthase and indoleglycerolphosphate synthase)have been determined in a wild type strain of Saccharomyces cerevisiae and in mutants with altered regulatory properties.
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Olshan AR, Gross SR. Role of the leu-3 cistron in the regulation of the synthesis of isoleucine and valine biosynthetic enzymes of Neurospora. J Bacteriol 1974; 118:374-84. [PMID: 4828304 PMCID: PMC246768 DOI: 10.1128/jb.118.2.374-384.1974] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The production by Neurospora of the enzymes of isoleucine and valine synthesis in response to specific end product-derived signals depends upon the presence of an effective leu-3 regulatory product and its effector alpha-isopropylmalate (alpha-IPM). In leu-3(+) strains, threonine deaminase production is repressed as a function of available isoleucine, acetohydroxy acid synthetase as a function of valine, and the isomeroreductase and dihydroxy acid dehydratase as a function of isoleucine and leucine. In the absence of an effective leu-3 regulatory product, alpha-isopropylmalate, or both, the production of isoleucine and valine biosynthetic enzymes is fixed at or near fully repressed levels even under conditions of severe end product limitation. Thus, in addition to its involvement in the regulation of expression of the three structural genes of leucine synthesis, the leu-3 alpha-IPM regulatory product is necessary for full expression of at least four genes specifying the structure of the enzymes of isoleucine and valine synthesis. It is suggested that the leu-3 alpha-IPM regulatory element may facilitate transcription of the genetically dispersed cistrons either by imposing specificity on ribonucleic acid polymerase for structurally similar promoters adjacent to each of the cistrons or by "opening" promoters after interaction with nearly identical stretches of deoxyribonucleic acid near each of the structural genes.
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Schürch A, Miozzari J, Hütter R. Regulation of tryptophan biosynthesis in Saccharomyces cerevisiae: mode of action of 5-methyl-tryptophan and 5-methyl-tryptophan-sensitive mutants. J Bacteriol 1974; 117:1131-40. [PMID: 4360539 PMCID: PMC246593 DOI: 10.1128/jb.117.3.1131-1140.1974] [Citation(s) in RCA: 141] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
In a wild-type strain of Saccharomyces cerevisiae the tryptophan analogue dl-5-methyl-tryptophan (5MT) causes only a slight reduction of the growth rate. Uptake experiments indicate that the limited inhibition is partly due to low levels of 5MT inside the cell. On the other hand, this low concentration of 5MT leads to an increase in the activity of the tryptophan-biosynthetic enzymes. Evidence is presented that suggests that 5MT acts primarily through feedback inhibition of anthranilate synthase, the first enzyme of the pathway. A number of 5MT-sensitive mutants have been isolated, characterized, and assigned to one of the following three classes: class I, strains with altered activity and/or feedback sensitivity of anthranilate synthase; class II, strains with elevated uptake of 5MT; class III, mutants with altered regulation of the tryptophan-biosynthetic enzymes, which do not exhibit increases in activity in the presence of 5MT. This failure to exhibit increased enzyme activities in mutants of class III can also be observed after tryptophan starvation. Two mutants of class III show high sensitivity towards 3-amino-1,2,4-triazole. They can not exhibit derepression of some histidine- and arginine-biosynthetic enzymes under conditions that lead to an increase in these same enzymes in the wild-type strain.
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Whitehouse JM, Smith DA. Methionine and vitamin B 12 repression and precursor induction in the regulation of homocysteine methylation in Salmonella typhimurium. MOLECULAR & GENERAL GENETICS : MGG 1973; 120:341-53. [PMID: 4568842 DOI: 10.1007/bf00268148] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Ryan ED, Tracy JW, Kohlhaw GB. Subcellular localization of the leucine biosynthetic enzymes in yeast. J Bacteriol 1973; 116:222-5. [PMID: 4355481 PMCID: PMC246411 DOI: 10.1128/jb.116.1.222-225.1973] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
When baker's yeast spheroplasts were lysed by mild osmotic shock, practically all of the isopropylmalate isomerase and the beta-isopropylmalate dehydrogenase was released into the 30,000 x g supernatant fraction, as was the cytosol marker enzyme, glucose-6-phosphate dehydrogenase. alpha-Isopropylmalate synthase, however, was not detected in the initial supernatant, but could be progressively solubilized by homogenization, appearing more slowly than citrate synthase but faster than cytochrome oxidase. Of the total glutamate-alpha-ketoisocaproate transaminase activity, approximately 20% was in the initial soluble fraction, whereas solubilization of the remainder again required homogenization of the spheroplast lysate. Results from sucrose density gradient centrifugation of a cell-free particulate fraction and comparison with marker enzymes suggested that alpha-isopropylmalate synthase was located in the mitochondria. It thus appears that, in yeast, the first specific enzyme in the leucine biosynthetic pathway (alpha-isopropylmalate synthase) is particulate, whereas the next two enzymes in the pathway (isopropylmalate isomerase and beta-isopropylmalate dehydrogenase) are "soluble," with glutamate-alpha-ketoisocaproate transaminase activity being located in both the cytosol and particulate cell fractions.
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Brooks CJ, DeBusk AG. Cellular compartmentation of aromatic amino acids in Neurospora crassa. I. Occupation of a protein synthesis pool by phenylalanine in Tyr-1 mutants. Biochem Genet 1973; 10:90-103. [PMID: 4270570 DOI: 10.1007/bf00485751] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Calhoun DH, Pierson DL, Jensen RA. The regulation of tryptophan biosynthesis in Pseudomonas aeruginosa. MOLECULAR & GENERAL GENETICS : MGG 1973; 121:117-32. [PMID: 4632776 DOI: 10.1007/bf00277526] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Ratzkin B, Arfin S, Umbarger HE. Isoleucine and valine metabolism in Escherichia coli. 18. Induction of acetohydroxy acid isomeroreductase. J Bacteriol 1972; 112:131-41. [PMID: 4562389 PMCID: PMC251388 DOI: 10.1128/jb.112.1.131-141.1972] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The regulation by substrate induction of the acetohydroxy acid isomeroreductase was studied in Escherichia coli. Induction was inhibited by chloramphenicol and rifampin. The addition of rifampin resulted in a decay of the capacity to form isomeroreductase. This was attributed to the breakdown of the isomeroreductase messenger, which had a half-life of about 45 sec at 37 C. Induction of isomeroreductase was enhanced by including glucose in the medium. This effect was shown to be due in part to the lowering of the pH of the medium, which presumably made inducer entry more rapid.
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Brooks CJ, DeBusk BG, DeBusk AG, Catcheside DE. A new class of p-fluorophenylalanine-resistant mutants in Neurospora crassa. Biochem Genet 1972; 6:239-54. [PMID: 4269807 DOI: 10.1007/bf00486118] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Mutation and "reversion" at the leu-5 locus of neurospora and its effect on the cytoplasmic and mitochondrial leucyl-tRNA synthetases. Biochem Genet 1971; 5:505-16. [PMID: 4940374 DOI: 10.1007/bf00485668] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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The Regulation of Branched and Converging Pathways. ACTA ACUST UNITED AC 1971. [DOI: 10.1016/b978-0-12-152803-4.50007-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Caroline DF, Davis RH. Pyrimidine synthesis in Neurospora crassa: regulation of enzyme activities. J Bacteriol 1969; 100:1378-84. [PMID: 5361219 PMCID: PMC250345 DOI: 10.1128/jb.100.3.1378-1384.1969] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
The regulation of several enzymes involved in pyrimidine biosynthesis in Neurospora crassa has been studied. Elevation of ATCase (l-aspartate carbamoyltransferase) activity is found in all pyrimidine-requiring mutants when they are starved for uridine. DHOase (dihydroorotase) is an unstable enzyme, and it is impossible to conclude what type of regulation, if any, controls this enzyme. DHOdehase (dihydroorotate dehydrogenase) activity shows a marked elevation in uridine-starved pyr-2 cultures, a mutant blocked late in the pathway. Several mutants blocked early in the pathway show much smaller increases in DHOdehase activity and possible explanations for this are discussed. Differences in the modes of regulation of the pyrimidine biosynthetic pathways in various organisms are compared.
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Magee PT, Hereford LM. Multivalent repression of isoleucine- valine biosynthesis in Saccharomyces cerevisiae. J Bacteriol 1969; 98:857-62. [PMID: 5788713 PMCID: PMC315264 DOI: 10.1128/jb.98.3.857-862.1969] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Regulation of the biosynthesis of four of the five enzymes of the isoleucine-valine pathway was studied in Saccharomyces cerevisiae. A method is described for limiting the growth of a leucine auxotroph by using valine as a competitor for the permease. Limitation for isoleucine and valine was accomplished by the use of peptides containing these amino acids conjugated with glycine as nutritional supplements for auxotrophs. The enzymes were repressed on synthetic medium containing isoleucine, valine, and leucine, as well as on broth supplemented with these amino acids. Limitation for any of the three branched-chain amino acids led to derepression of the isoleucine-valine biosynthetic pathway. Maximal derepression ranged from 3-fold for threonine deaminase to approximately 10-fold for acetohydroxyacid synthase. (Two of the enzymes, acetohydroxyacid synthase and dihydroxyacid dehydrase, may be controlled by a mechanism different from that regulating threonine deaminase.) Possible molecular mechanisms for multivalent repression are discussed.
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Botsford JL, Parks LW. Serine transhydroxymethylase in methionine biosynthesis in Saccharomyces cerevisiae. J Bacteriol 1969; 97:1176-83. [PMID: 5776524 PMCID: PMC249832 DOI: 10.1128/jb.97.3.1176-1183.1969] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
Serine transhydroxymethylase appears to be the first enzyme in the synthesis of the methyl group of methionine. Properties of serine transhydroxymethylase activity as assayed by the production of formaldehyde were correlated with properties of cell-free extracts for the methylation of homocysteine deriving the methyl group from the beta-carbon of serine. The reaction required pyridoxal phosphate and tetrahydrofolic acid, and was characterized in cell-free extracts with respect to Michaelis constant, pH optimum, incubation time, and optimal enzyme concentration. The activity was sensitive to inhibition by methionine, and to a much greater extent by S-adenosylmethionine. Serine transhydroxymethylase and the methylation of homocysteine reactions were not repressed by methionine and were stimulated by glycine. The activities of cell-free extracts for these reactions were significantly higher in cells in exponential than in stationary growth. When cells were grown in 10 mm glycine, the activities remained high throughout the culture cycle. The data indicated that glycine rather than methionine is involved in the control of the formation of the enzyme.
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Regulation of the Biosynthesis of the Branched-Chain Amino Acids. ACTA ACUST UNITED AC 1969. [DOI: 10.1016/b978-0-12-152801-0.50009-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/13/2023]
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Satyanarayana T, Umbarger HE, Lindegren G. Biosynthesis of branched-chain amino acids in yeast: regulation of leucine biosynthesis in prototrophic and leucine auxotrophic strains. J Bacteriol 1968; 96:2018-24. [PMID: 5724970 PMCID: PMC252553 DOI: 10.1128/jb.96.6.2018-2024.1968] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The first enzyme in the biosynthesis of leucine in yeast, alpha-isopropylmalate synthetase, is inhibited by l-leucine. In a mutant resistant to the analogue 5',5',5'-trifluoroleucine, the enzyme is markedly resistant to inhibition by l-leucine. Growth ing the presence of exogenous l-leucine results in repression of the second and third enzymes of the pathway. The first enzyme is not repressed unless both l-leucine and l-threonine are supplied in the medium. Comparison of levels of the remaining two enzymes in leucine auxotrophs grown under conditions of leucine excess and leucine limitation reveals deviations from the wild-type derepression pattern in some mutants. In some, repression of the synthetase by leucine alone was observed. In others, the repressibility of the dehydrogenase was lost. It is unlikely that these deviations were due to the same primary mutational event that caused leucine auxotrophy. No mutants were found in which an altered gene was recognized to be clearly responsible for the level of the leucine-forming enzymes.
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Satyanarayana T, Umbarger HE, Lindegren G. Biosynthesis of branched-chain amino acids in yeast: correlation of biochemical blocks and genetic lesions in leucine auxotrophs. J Bacteriol 1968; 96:2012-7. [PMID: 5724969 PMCID: PMC252552 DOI: 10.1128/jb.96.6.2012-2017.1968] [Citation(s) in RCA: 42] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
The three enzymatic steps in the conversion of alpha-ketoisovalerate to alpha-ketoisocaproate were examined in wild-type and in leucine auxotrophic stocks of yeast. Procedures for the reliable assay of each of the enzymatic steps in crude extracts were devised. Crude extracts of the prototrophic haploid stock catalyzed all three enzymatic steps. Examination of a series of leucine auxotrophs permitted a correlation between the three enzymatic steps and the genetic lesions affecting 10 different loci. This examination revealed that a single locus (le-6) affected primarily alpha-isopropylmalate synthetase, the first step in the pathway. Lesions in six loci (le-1, le-4, le-5, le-7, le-8, and le-10) lead primarily to a deficiency in the activity of the second enzyme in the pathway, alpha-isopropylmalate isomerase. Stocks with lesions in three loci (le-2, le-3, and le-9) were primarily blocked in the third step of the pathway, catalyzed by beta-isopropylmalate dehydrogenase. The results with the mutants provide strong evidence that the pathway for leucine biosynthesis proposed by Strassman and his colleagues is the sole significant pathway in yeast.
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Abstract
Biochemical steps of the pyrimidine pathway have been found to be the same in yeast as in bacteria, and all except one step have been characterized. The activities of the first two enzymes, carbamoyl phosphate synthetase and aspartic transcarbamylase, are simultaneously controlled by feedback inhibition and repression. Moreover, these enzymes are coded by the same genetic region (ura-2) and seem to form a single enzymatic complex. The enzymes that follow later in the pathway are induced in a sequential way by the intermediary products and are insensitive to pyrimidine repression. The corresponding genes (ura-4, ura-1, ura-3) are not linked to each other or to ura-2, the gene for carbamoyl phosphate synthetase and aspartic transcarbamylase. Mutants that have simultaneously lost feedback inhibition by uridine triphosphate for carbamoyl phosphate synthetase and for aspartic transcarbamylase have been found and mapped in the gene ura-2.
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Pinsky L, Krooth RS. Studies on the control of pyrimidine biosynthesis in human diploid cell strains. II. Effects of 5-azaorotic acid, barbituric acid, and pyrimidine precursors on cellular phenotype. Proc Natl Acad Sci U S A 1967; 57:1267-74. [PMID: 5231733 PMCID: PMC224467 DOI: 10.1073/pnas.57.5.1267] [Citation(s) in RCA: 41] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
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Printz DB, Gross SR. An apparent relationship between mistranslation and an altered leucyl-tRNA synthetase in a conditional lethal mutant of Neurospora crassa. Genetics 1967; 55:451-67. [PMID: 6038419 PMCID: PMC1211401 DOI: 10.1093/genetics/55.3.451] [Citation(s) in RCA: 46] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
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Abstract
Burns, R. O. (Cold Spring Harbor Laboratories of Quantitative Biology, Cold Spring Harbor, N.Y.), J. Calvo, P. Margolin, and H. E. Umbarger. Expression of the leucine operon. J. Bacteriol. 91:1570-1576. 1966.-The four genes which specify the structure of the three enzymes specifically involved in the biosynthesis of leucine in Salmonella typhimurium constitute a single operon. Three types of control mutants have been delineated on the basis of their location on the Salmonella chromosome and the manner in which they coordinately affect the rates of synthesis of the pertinent enzymes. The three types of mutants correspond to operator-negative, operator-constitutive, and regulator-negative. The rate of synthesis of the enzymes can also be altered by varying the amount of leucine made available to the cell. Leucine can be effectively limited by limiting the supply of alpha-ketoisovalerate, but in doing so two of the three enzymes, alpha-isopropylmalate synthetase and isopropylmalate isomerase, are labilized. This observation was correlated with an in vivo diminution of the levels of the substrates of these enzymes and the fact that alpha-ketoisovalerate and alpha-isoporpylmalate protect the respective enzymes against thermal inactivation in vitro. The functional association of the structural genes is also illustrated by the presence of polarity mutations; that is, certain structural gene mutations lower the rates of synthesis of the enzymes specified by genes located distally to the mutated gene and the operator segment of the operon.
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