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  • 1
    ISSN: 1432-0983
    Keywords: Phycomyces blakesleeanus ; β-carotene ; End-product regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The regulation of carotenogenesis in the fungus Phycomyces blakesleanus is mediated by several gene products and influenced by light, retinol, and other external agents. De-regulation of the biosynthetic pathway is found in the deep-yellow carS mutants and the white carA mutants. The carA, carS recombinants are yellow; their β-carotene content is intermediate between that of strains carrying each of the two mutations. Mutagen exposure of a deep-yellow carS mutant led to the isolation of white double-mutants which become yellow in the presence of retinol. They carry two very closely linked mutations in the carS gene. When separated in different organisms, each of these mutations results in a deep-yellow phenotype. Our results support the idea that two gene products recognize the beta rings of β-carotene and shut off biosynthesis when enough β-carotene has been made. The modified gene product present in the white carS mutants stops synthesis in the absence of β-carotene.
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  • 2
    ISSN: 1432-0983
    Keywords: Nitrosoguanidine ; Comutation ; Yeast ; Chromosome replication pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Contrary to what happens in bacteria, mutations induced by nitrosoguanidine in yeast are not accompanied by an excess of mutations in nearby genes. We have investigated nitrosoguanidine mutagenesis in three regions of the yeast genome: the contiguous DNA segments HIS4A, HIS4B and HIS4C, located on chromosome III; ADE1 and CDC15 separated by about 3 map units on chromosome I; and CAN1, some 50 map units away from the centromere on chromosome V. Revertants at HIS4C never suffered mutations at HIS4A or HIS4B. Reversion at CDC15 did not affect the frequency of mutation at ADE1. No tsm mutations, leading to thermonsensitivity, were found in the immediate vicinity of the locus CAN1 after selecting for canavanine resistant mutants. However, as expected from nitrosoguanidine mutagenesis of replication points and the fixed pattern of chromosome replication, the induced tsm mutations seem not to map randomly over the yeast genome; in fact, two out of the three groups of such tsm mutations studied are located in the same chromosome arm as CAN1, indicating that these two regions are replicated at the same time as CAN1. Replication synchrony is less than perfect, since the tsm mutations of each group affect many different genes.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 11 (1987), S. 505-511 
    ISSN: 1432-0983
    Keywords: Gibberella fujikuroi ; Fusarium moniliforme ; Carotenoid mutants ; Neurosporaxanthin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The orange pigment neurosporaxanthin colours the mycelia of wild Gibberella fujijuori (Fusarium monifliforme) grown in the light, but is barely detectable in the dark. We have isolated carotenoid mutants from conidia exposed to N-methyl-N′-nitro-N-nitroso-guanidine and other mutagens. Specific blocks in the pathway are represented by white mutants accumulating phytoene and red mutants accumulating torulene; there are also mutants without carotenoids or with complex carotenoid mixtures. Regulatory mutants overproduce neurosporaxanthin, both in the light and in the dark. Other mutants contain considerable neurosporaxanthin in the dark, but less than in the light. The results bring out similarities between the carotenoid biosynthetic pathways of Gibberella and Phycomyces, and significant differences in their respective regulations.
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  • 4
    ISSN: 1432-072X
    Keywords: Carotenogenesis ; Regulation ; Phycomyces ; Retinol ; Phthalate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Wild-type Phycomyces blakesleeanus synthesizes the yellow pigment, beta-carotene. Colour mutants exhibit various alterations in the biosynthesis of beta-carotene or in its regulation. The presence of certain chemicals in the medium stimulates carotenogenesis in the wild type. We attribute different mechanisms of action to agents which stimulate or fail to stimulate different sets of mutants; this is the case of retinol and dimethyl phthalate. Dimethyl phthalate and veratrol are active on the same mutants, and therefore are likely to act in the same way. The main regulation of carotenogenesis, end-product inhibition, does not operate in the mutants of certain genes; these mutants are indifferent to retinol. By using a collection of retinoids we conclude that their action depends on their structural similarity to a part of the beta-carotene molecule. From these and other observations we propose that end-product inhibition of the pathway is mediated by a complex of beta-carotene and two gene products and that the retinoids compete with beta-carotene and prevent end-product inhibition.
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  • 5
    ISSN: 1617-4623
    Keywords: Spore germination ; Acetate ; Propionate ; Heat ; Trehalase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Exposure to heat, acetate, or propionate activates the spores of the fungus Phycomyces blakesleeanus and allows them to germinate. Using counterselection with the antibiotic N-glycosyl-polyfungin, seven mutants were isolated on the basis of decreased spore activation by acetate and two on the basis of decreased spore activation by propionate. The nine mutants showed decreased activation by both chemicals and by heat, increased heat lethality, and altered patterns of trehalase activation. These and other observations indicate that spore activation by the three agents and spore death by heat are mediated by the same cellular component(s), which is probably involved in the regulation of cyclic AMP concentration.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Mycoscience 40 (1999), S. 307-310 
    ISSN: 1618-2545
    Keywords: Blakeslea trispora ; carotene ; cyclase inhibitors ; lycopene cyclization ; sexual activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Fungi produce and accumulate various carotenoids. Mycelia of the ZygomyceteBlakeslea trispora contained β-carotene and its precursors γ-carotene and lycopene. When strains of opposite sex grew together, the β-carotene concentration increased fourfold, that of γ-carotene remained unchanged, and other intermediates practically disappeared. The inhibitors nicotine, 2-(4-chlorophenylthio)-triethylamine, α-picoline, and imidazole increased the concentrations of lycopene and γ-carotene and decreased those of β-carotene. From our quantitative results, we conclude thatBlakeslea has two pathways for lycopene metabolism, of which other fungi have only one or the other. The main one, two cyclizations from lycopene to β-carotene, is carried out by an enzyme dimer, is stimulated by sexual interaction, and is sensitive to the inhibitors. The other pathway, a cyclization to γ-carotene is not affected by mating or the inhibitors.
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  • 7
    ISSN: 1617-4623
    Keywords: Gibberella fujikuroi ; Heterologous transformation ; Nitrate reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A transformation system for Gibberella fujikuroi based on the Aspergillus niger nitrate reductase gene (niaD) was developed. A strain (designated SG140) carrying a non-reverting niaD mutation (niaD11) was generated by screening mutagenised cells for non-growth on nitrate as sole nitrogen source. Transformation frequencies of 1–2 transformants per μg DNA were observed when strain SG140 was transformed to nitrate utilisation. Southern blot analyses of niaD+ transformants showed that the vector DNA sequences were integrated into the chromosomal DNA. The results demonstrate that the A. niger niaD gene is expressed in G. fujikuroi.
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  • 8
    ISSN: 1617-4623
    Keywords: Phycomyces ; Chitin synthetase ; Nikkomycin ; N-acetylglucosamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mutants resistant to nikkomycin, an inhibitor of chitin biosynthesis, were isolated after exposure of wild-type spores of the fungus Phycomyces blakesleeanus to N-methyl-N′-nitro-N-nitrosoguanidine. Genetic analysis revealed that nikkomycin resistance was due to mutations in a single gene, chsA. Mutants and wild type grew equally well in the absence of nikkomycin. In contrast to the wild type, whose spore germination and mycelial growth were inhibited by 5 μM nikkomycin, chsA mutants grew reasonably well in the presence of 50 μM nikkomycin. Chitin synthesis in vivo was much less affected by the drug in the mutants than in the wild type. Resistance was not due to impaired uptake or detoxification of the drug. Analysis of the kinetics of chitin synthesis in vitro showed that the mutants had a decreased Ka for the allosteric activator, N-acetylglucosamine, and gross alterations in nikkomycin inhibition kinetics. These results indicate that chsA is the structural gene for chitin synthetase, or at least for the polypeptide that bears the catalytic and allosteric sites.
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  • 9
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Production of bikaverin and gibberellins by Gibberella fujikuroi started after depletion of the nitrogen source, but not after depletion of phosphate. Despite this similarity, the regulation of both pathways by nitrogen involved two different mechanisms. This conclusion was supported by the fact that the production of bikaverin, in contrast to the gibberellins, was not inhibited by nitrate in a mutant that could not utilize it. The different regulation of both pathways was clearly demonstrated by a mutant that overproduced bikaverin but lacked gibberellins. An optimal bikaverin production required a low pH, with a sharp drop at about pH 5. The syntheses of fungal secondary metabolites, such as bikaverin and gibberellins, are not subject to common regulation, but respond to various combinations of signals, such as nitrogen availability, nitrate and the pH of the medium.
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 25 (2001), S. 0 
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Phycomyces has been in the laboratories for about 140 years, sometimes following trends and fashions, but often anticipating them. Researchers have been attracted by the sensitive and precise responses of Phycomyces to light and other stimuli, coupled with easy manipulations and good adaptation to laboratory life. It is a simple prototype of the many organisms that use light as a source of information but not as a significant source of energy. Growth, development, genetics, and carotene production have been other subjects of pioneering research. Phycomyces was the second organism, after us, known to require a vitamin. It was one of the first organisms in the research on spontaneous mutants and the second, after Drosophila, in which mutations were induced artificially. It was used to coin the concept and the name of heterokaryosis. Phycomyces heterokaryons offer unique experimental possibilities, for instance in the study of gene function in vivo and the causes of cell death. An overall impression of parsimony and combinatorial gene usage arises from the genetic analysis of the complex functions of this fungus. The main subjects of recent attention have been the various reactions to light, gravitropism, and some aspects of metabolism, particularly the production of carotene. Interest in Phycomyces is slacking because of the repeated failures at transforming it stably with exogenous DNA.
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