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Regulation of nitrogen fixation in Azorhizobium caulinodans: identification of a fixK-like gene, a positive regulator of nifA

Abstract : The nucleotide sequence of a 1 kb fragment upstream of Azorhizobium caulinodans fixL was established. An open reading frame of 744 bp was identified as a fixK homologue. A kanamycin cartridge was inserted into the cloned fixK-like gene and recombined into the host genome. The resulting mutant was Nif-Fix-, suggesting that FixK was required for nitrogen fixation both in symbiotic conditions and in the free-living state. Using a pfixK-lacZ fusion, the FixLJ products were shown to control the expression of fixK. Using a pnifA-lacZ fusion, the FixK product was shown to regulate positively the transcription of nifA in bacteria grown in the free-living state. In addition, a double ntrC-fixL mutant was constructed and was shown to be completely devoid of nitrogenase activity. A model of regulation, based on these data, is presented and might explain the unusual ability of A. caulinodans to fix nitrogen both under symbiotic conditions and in the free-living state.
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Submitted on : Thursday, May 5, 2022 - 2:01:58 PM
Last modification on : Friday, May 6, 2022 - 3:38:37 AM

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Pierre-Alexandre Kaminski, K. Mandon, F. Arigoni, N. Desnoues, C. Elmerich. Regulation of nitrogen fixation in Azorhizobium caulinodans: identification of a fixK-like gene, a positive regulator of nifA. Molecular Microbiology, Wiley, 1991, 5 (8), pp.1983-1991. ⟨10.1111/j.1365-2958.1991.tb00820.x⟩. ⟨pasteur-03659895⟩

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