Ammonium repression of the nitrite-nitrate ( nasAB ) assimilatory operon of Azotobacter vinelandii is enhanced in mutants expressing the nifO gene at high levels |
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Authors: | J C Gutierrez E Santero and M Tortolero |
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Institution: | (1) Departamento de Microbiologia, Faculdad de Biologìa, Universidad de Sevilla, Ap. 1095, E-41080 Sevilla, Spain, ES;(2) Departamento de Genética, Facultad de Biologìa, Universidad de Sevilla, Ap. 1095, E-41080 Sevilla, Spain, ES |
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Abstract: | A number of Tn5 mutants were isolated which were unable to fix nitrogen and showed enhanced ammonium repression of the nitrate/nitrite assimilation
genes. They also had reduced nitrate reductase activity under fully inducing conditions. Insertions were localized within
the nifB gene, and inability to fix nitrogen was shown to be due to disruption of the nifB gene. However, enhanced ammonium repression proved to be the result of constitutive expression of the downstream nifO gene from an `out' promoter present in Tn5. Our results suggest that molybdenum metabolism might function as a regulatory factor that acts through the nitrate reductase.
Received: 4 December 1996 / Accepted: 27 March 1997 |
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Keywords: | nasAB Chlorate-resistant mutants nifO Nitrogen fixation mutants |
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