Molybdate repair of molybdopterin deficient mutants from Chlamydomonas reinhardtii |
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Authors: | Emilio Fernández Miguel Aguilar |
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Institution: | (1) Departamento de Bioquímica, Biologia Molecular y Fisiologia, Facultad de Ciencias, Universidad de Córdoba, E-14071 Córdoba, Spain;(2) Present address: Department of Genetics and Cell Biology, 250 Biological Sciences Center, University of Minnesota, 1445 Gortner Avenue, 55108 St. Paul, MN, USA |
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Abstract: | 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. |
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Keywords: | Molybdenum cofactor Nitrate reductase Chlamydomonas reinhardth |
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