Disease relevance of fixR

• A region of the chromosome of Agrobacterium tumefaciens 11 kb long containing two operons required for cellulose synthesis and a part of a gene homologous to the fixR gene of Bradyrhizobium japonicum has been sequenced [1].

High impact information on fixR

• Between the start of transcription and the nifA gene an open reading frame of 278 codons was found and named fixR [2].
• Dual control of the Bradyrhizobium japonicum symbiotic nitrogen fixation regulatory operon fixR nifA: analysis of cis- and trans-acting elements [3].
• By using chromosomally integrated fixR-lacZ fusions, the level of expression of the fixR nifA operon was found to be fivefold higher under reduced oxygen tension than under aerobiosis [3].
• This led to the identification of 11 critical nucleotides within a 17 bp minimal RegR binding site centered at position -64 upstream of the fixR-nifA transcription start site [4].

Biological context of fixR

• Based on these data, we propose a model for the regulation of nitrogen fixation genes in B. japonicum that involves dual positive control of the fixR nifA operon [3].
• Aerobic expression of the fixR nifA operon in Bradyrhizobium japonicum was shown to depend on a cis-acting, promoter-upstream DNA sequence located between the -24/-12 promoter and position -86 relative to the transcription start site [3].
• Basal expression of this operon depends on the response regulator RegR and a DNA element located around position -68 in the fixR-nifA promoter region [5].

References