The Bradyrhizobium japonicum fixBCX operon: identification of fixX and of a 5' mRNA region affecting the level of the fixBCX transcript

Molecular Microbiology
M GublerH Hennecke

Abstract

The Bradyrhizobium japonicum fixX gene was identified and shown to be essential for symbiotic and free-living, microaerobic nitrogen fixation. The fixX gene encodes a ferredoxin-like protein which may be involved in a redox process (electron transport?) essential for nitrogenase activity. This gene was localized downstream of fixC and its expression was dependent on the fixB promoter, providing evidence for the existence of a fixBCX operon. Mutagenesis and sequence analysis of the unusually long, 709bp leader region between the fixB promoter and the fixB structural gene did not reveal the presence of a nif or fix gene that was absolutely essential for nitrogen fixation. However, a short open reading frame (ORF) within this region encoding a polypeptide of 35 amino acids (ORF35) was shown to be efficiently translated. Chromosomal deletion of a 400bp DNA fragment covering ORF35 resulted in a three-fold reduction of the fixBCX mRNA level, which in turn also reduced the nitrogen fixation activity of this mutant. This suggests a possible post-transcriptional control mechanism for the expression of the fixBCX operon involving the stabilization of fixBCX mRNA by ribosomes actively translating ORF35.

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Citations

Jan 1, 1991·Archives of Microbiology·T M Ramseier, M Göttfert
Dec 10, 1996·Proceedings of the National Academy of Sciences of the United States of America·D L RobertsJ J Kim
Jan 31, 2018·Nature Reviews. Microbiology·Philip PooleJason Terpolilli
Aug 16, 2017·Journal of Bacteriology·Amaya M Garcia CostasJohn W Peters
Feb 1, 1993·Journal of Bacteriology·C KündigM Göttfert
Sep 1, 1994·Microbiological Reviews·H M Fischer
Jun 11, 2021·Molecular Plant-microbe Interactions : MPMI·Isabel U C WebbPhilip S Poole

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