Regulation of nif gene expression in Enterobacter agglomerans: nucleotide sequence of the nifLA operon and influence of temperature and ammonium on its transcription
✍ Scribed by Siddavattam, Dayananda ;Steibl, Hans-Dieter ;Kreutzer, Roland ;Klingmüller, Walter
- Publisher
- Springer
- Year
- 1995
- Tongue
- English
- Weight
- 757 KB
- Volume
- 249
- Category
- Article
- ISSN
- 0026-8925
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✦ Synopsis
The nucleotide sequence of a plasmid-borne 3.9 kb XhoI-SmaI fragment comprising the 3'-region of the nifM gene, the nifL and nifA genes and the 5'region of nifB gene of Enterobacter a991omerans was determined. The genes were identified by their homology to the corresponding n/f genes of Klebsiella pneumoniae. A typical cyS4-dependent promoter and a consensus NtrC-binding motif were identified upstream of nifL. The predicted amino acid sequence of NifL showed close similarities to NifL of K. pneumoniae and Azotobacter vinelandii. However, no histidine residue was found to correspond to histidine-304 of A.
vinelandii NifL, which had been proposed to be required for the repressor activity of NifL. The NifA sequence with a putative DNA binding motif (Q(x3) A(x3) G(xs)I) and an ATP binding site in the C-terminal and central domains, respectively, resembles that of other known NifA proteins. The function of thenifL and nifA genes was demonstrated in vivo using a binary plasmid system by their ability to activate a nifH promoter-lacZ fusion at different temperatures and concentrations of NH~-. Maximal promoter activity occurred at 25 ° C, and it appears that the sensitivity of NifA to elevated temperatures is independent of NifL.
The expression of nifL inhibited promoter activity in the presence of NifA when the initial NH2 concentration in the medium exceeded 4 mM.