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Hill, S, Austin, S, Eydmann, T, Jones, T and Dixon, R (1996) Azotobacter vinelandii NIFL is a flavoprotein that modulates transcriptional activation of nitrogen-fixation genes via a redox-sensitive switch. Proc. Natl. Acad. Sci. U.S.A. 93:2143-8


The NIFL regulatory protein controls transcriptional activation of nitrogen fixation (nif) genes in Azotobacter vinelandii by direct interaction with the enhancer binding protein NIFA. Modulation of NIFA activity by NIFL, in vivo occurs in response to external oxygen concentration or the level of fixed nitrogen. Spectral features of purified NIFL and chromatographic analysis indicate that it is a flavoprotein with FAD as the prosthetic group, which undergoes reduction in the presence of sodium dithionite. Under anaerobic conditions, the oxidized form of NIFL inhibits transcriptional activation by NIFA in vitro, and this inhibition is reversed when NIFL is in the reduced form. Hence NIFL is a redox-sensitive regulatory protein and may represent a type of flavoprotein in which electron transfer is not coupled to an obvious catalytic activity. In addition to its ability to act as a redox sensor, the activity of NIFL is also responsive to adenosine nucleotides, particularly ADP. This response overrides the influence of redox status on NIFL and is also observed with refolded NIFL apoprotein, which lacks the flavin moiety. These observations suggest that both energy and redox status are important determinants of nif gene regulation in vivo.


PubMed PMC39924


Adenosine Diphosphate/metabolism; Azotobacter vinelandii/genetics; Bacterial Proteins/physiology; Flavin-Adenine Dinucleotide/physiology; Flavoproteins/physiology; Gene Expression Regulation, Bacterial; Genes, Bacterial; Nitrogen Fixation/genetics; Protein Conformation; Structure-Activity Relationship; Transcription, Genetic



Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status



GO:0006355: regulation of transcription, DNA-templated

ECO:0000314: direct assay evidence used in manual assertion


Seeded From UniProt



GO:0006355: regulation of transcription, DNA-dependent



Figure 2:NIFL is a regulatory protein that directs the transcriptional activities of nitrogen fixation genes. It does this by interacting with NIFA, which is an enhancer binding protein. Since previous research has shown that NIFL is a flavoprotein, this gene gets reduced in the presence of sodium dithionite. Transcription in inhibited when NIFL is oxidized. Transcriptional activiation can be measured by looking at the formation of open promoter complexes. This figure shows that sodium dithionite did not affect NIFA since the open promoter complexes were formed with or without the addition of sodium dithionite. This figure also shows that with the addition of sodium dithionite to NIFL and NIFA together, which would mean that NIFL is reduced, open promoter complexes were able to be formed. On the other hand, without sodium dithionite, NIFL is oxidized, and no open promoter complexes could be formed.

CACAO 2693

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