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  • 1
    Electronic Resource
    Electronic Resource
    Different forms of molybdenum cofactor inVicia faba seeds: The presence of molybdenum cofactor carrier protein and its purification (1997)
    Springer
    Planta 201 (1997), S. 64-70 
    Details
    ISSN: 1432-2048
    Keywords: Molybdate ; Molybdenum cofactor ; Nitrate reductase ; Vicia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract There were significant differences in the contents of molybdenum cofactor (Mo-co), both in a low-molecular-mass form (free Mo-co) and in a protein-bound form, in seeds of sevenVicia faba genotypes. Low-molecular-mass Mo-co species present in the extracts were detected by their ability to reactivate, through a dialysis membrane, aponitrate reductase from theNeurospora crassa nit-1 mutant. In extracts of all genotypes tested, the amount of Mo-co capable of directly reactivating nitrate reductase of theN. crassa nit-1 mutant was always much higher than that of low-molecular-mass Moco. These data cannot be explained by considering, as traditionally, that Mo-co detected directly, i.e. without any previous treatment for its release from Mo-coproteins, corresponds to free low-molecular mass Mo-co. A protein which bound Mo-co was purified to electrophoretic homogeneity. This protein consisted of a single 70-kDa polypeptide chain and carried a Mo-co that could be efficiently released when in contact with aponitrate reductase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01258681
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  • 2
    Electronic Resource
    Electronic Resource
    Molybdate repair of molybdopterin deficient mutants from Chlamydomonas reinhardtii (1987)
    Springer
    Current genetics 12 (1987), S. 349-355 
    Details
    ISSN: 1432-0983
    Keywords: Molybdenum cofactor ; Nitrate reductase ; Chlamydomonas reinhardth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The phenotypically wild strain I3 of Chlamydomonas reinhardtii, carrying a cryptic mutation at the nit-6 locus, was distinguished from strains 21gr (cryptic mutant at nit-5) and 6145c (wild type) because of the ability of I3 to grow on nitrate media containing 2mM tungstate. Molybdopterin-cofactor (MoCo) mutants 102 (double mutant at nit-5 and nit-6) and 104 (mutant at nit-4) grew on nitrate media supplemented with high concentrations of molybdate, although final cell densities were 40–60% lower and generation times 3.5 to six fold longer than for wild type. Under these conditions, nitrate reductase (NR) activity of the mutants, when measured either in situ or in vitro, was practically undetectable. The MoCo defective mutant 307 (nit-3) was not molybdate repairable. Although NR activity was not restored in vitro by molybdate in any of the MoCo− mutant strains, their extracts had free NR-diaphorase subunits together with NR-subunits assembled into high molecular weight species. Our results indicate that: a) nit-4, nit-5 and nit-6 loci are responsible for molybdate processing in the cell; b) nit-3 may encode a component of the pterin moiety biosynthetic route; c) NR subunits can assemble in the presence of an inactive MoCo; d) high concentrations of molybdate can replace partially in vivo but not in vitro the function of nit-4 and the combined function(s) of the nit-5 and nit-6 gene products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00405757
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  • 3
    Electronic Resource
    Electronic Resource
    In vivo complementation analysis of nitrate reductase-deficient mutants in Chlamydomonas reinhardtii (1986)
    Springer
    Current genetics 10 (1986), S. 397-403 
    Details
    ISSN: 1432-0983
    Keywords: Chlamydomonas reinhardtii ; Nitrate reductase ; Complementation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In vivo complementation between different wild and mutant strains defective for nitrate assimilation has been performed by isolating diploid strains from the appropriate crosses. Twenty-two diploids homozygous or heterozygous with respect to nitrate reduction and able to grow on nitrate medium were obtained and their diploid character demonstrated from analyses of mating type, cell volume, nuclear size and progeny of crosses with haploid wild-type. All diploids were assayed for overall- and terminal-nitrate reductase (NR) activity and for the occurrence of the NR-diaphorase subunit. Data on NR activities in heterozygotes carrying mutation(s) in structural gene(s) (nit-1 or nit-1a, nit-1b) agree with the heteromultimeric nature of the enzyme complex previously described (Franco et al. (1984) EMBO J 3: 1403–1407), and indicate that subunits are exchangeable to form hybrid enzymes. In addition, in vitro complementation tests with mutant nit-1 of C. reinhardtii indicate that this mutant has defective NR-diaphorase subunits but intact terminal subunits. Super-repression caused by the mutant allele nit-2 is suppressed by the wild allele in heterozygotes, which suggests a positive control by the nit-2 product on structural gene(s) transcription. Mutant alleles of genes for the biosynthesis of molybdenum-containing cofactor, either nit-4 or nit-5 and nit-6, were recessive in diploids carrying them. The mutant allele of nit-3, from strain 307, was codominant in all heterozygotes suggesting that nit-3 codes for a protein whose activity is limiting for the molybdenum-cofactor biosynthetic pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00418413
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  • 4
    Electronic Resource
    Electronic Resource
    Genetic analysis of nitrate reductase-deficient mutants in Chlamydomonas reinhardii (1984)
    Springer
    Current genetics 8 (1984), S. 635-640 
    Details
    ISSN: 1432-0983
    Keywords: Chlamydomonas reinhardii ; Nitrate reductase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Six mutants (305, 301, 203, 307, 104 and 102) of Chlamydomonas reinhardii, all defective in nitrate reductase (NR) activity, have been genetically analyzed. All except 102 carry single Mendelian mutations. Mutant 305, defective in diaphorase activity and mutant 301, defective in terminal enzyme activity, did not give rise to wild-type recombinants when crossed to each other or with the nit-1 mutant isolated from strain 137c (which is actually a double mutant nit-1 nit-2). Nit-1 was shown to lack both diaphorase and terminal activities. Whether the mutated sites in 305 and 301 are located in a unique cistron (nit-1) or in two adjacent cistrons (nit-1a and nit-1b) coding for a diaphorase subunit and a terminal subunit of NR is discussed in the light of previous biochemical findings. The 203 mutation affecting a regulatory gene did not recombine with nit-2, the other mutated locus present in strain 137c. Mutants 307, 104 and 102, all lacking molybdenum cofactor for both NR and xanthine dehydrogenase, where shown to be affected in different loci. The genes mutated in 307 and 104 have been designated nit-3 and nit-4, respectively. The 102 strain is mutated in two non-linked loci, nit-5 and nit-6, with both mutations required to confer the mutant phenotype. One of these cryptic mutations is present in the “wild” strain 21gr. The results indicate that at least six or seven loci are involved in the production of an active NR enzyme: one (nit-1) or two (nit-1a and nit-1b) cistrons to produce the NR apoproteins responsible for the partial activities diaphorase and terminal, one locus (nit-2) for the regulation of NR synthesis, and four loci (nit-3, nit-4, nit-5 and nit-6) to produce the molybdenum cofactor. The loci nit-1a and nit-2 seem to correspond to the nit-A and nit-B loci described by Nichols and Syrett (J Gen Microbiol 108:71–77, 1978).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00395710
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  • 5
    Electronic Resource
    Electronic Resource
    Toxicity of and mutagenesis by chlorate are independent of nitrate reductase activity in Chlamydomonas reinhardtii (1993)
    Springer
    Molecular genetics and genomics 237 (1993), S. 429-438 
    Details
    ISSN: 1617-4623
    Keywords: Chlamydomonas reinhardtii ; Chlorate resistance ; Nitrate reductase ; Nitrate transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Spontaneous chlorate-resistant (CR) mutants have been isolated from Chlamydomonas reinhardtii wildtype strains. Most of them, 244, were able to grow on nitrate minimal medium, but 23 were not. Genetic and in vivo complementation analyses of this latter group of mutants indicated that they were defective either at the regulatory locus nit-2, or at the nitrate reductase (NR) locus nit-1, or at very closely linked loci. Some of these nit-1 or nit-2 mutants were also defective in pathways not directly related to nitrate assimilation, such as those of amino acids and purines. Chlorate treatment of wild-type cells resulted in both a decrease in cell survival and an increase in mutant cells resistant to a number of different chemicals (chlorate, methylammonium, sulphanilamide, arsenate, and streptomycin). The toxic and mutagenic effects of chlorate in minimal medium were not found when cells were grown either in darkness or in the presence of ammonium, conditions under which nitrate uptake is drastically inhibited. Chlorate was also able to induce reversion of nit − mutants of C. reinhardtii, but failed to produce His + revertants or Arar mutants in the BA-13 strain of Salmonella typhimurium. In contrast, chlorate treatment induced mutagenesis in strain E1F1 of the phototrophic bacterium Rhodobacter capsulatus. Genetic analyses of nitrate reductase-deficient CR mutants of C. reinhardtii revealed two types of CR, to low (1.5 mM) and high (15 mM) chlorate concentrations. These two traits were recessive in heterozygous diploids and segregated in genetic crosses independently of each other and of the nit-1 and nit-2 loci. Three her loci and four lcr loci mediating resistance to high (HC) and low (LC) concentrations of chlorate were identified. Mutations at the nit-2 locus, and deletions of a putative locus for nitrate transport were always epistatic to mutations responsible for resistance to either LC or HC. In both nit + and nit − chlorate-sensitive (CS) strains, nitrate and nitrite gave protection from the toxic effect of chlorate. Our data indicate that in C. reinhardtii chlorate toxicity is primarily dependent on the nitrate transport system and independent of the existence of an active NR enzyme. At least seven loci unrelated to the nitrate assimilation pathway and mediating CR are thought to control indirectly the efficiency of the nitrate transporter for chlorate transport. In addition, chlorate appears to be a mutagen capable of inducing a wide range of mutations unrelated to the nitrate assimilation pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00279448
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