Regulatory proteins and cis-acting elements involved in the transcriptional control of Rhizobium etli reiterated nifH genes.
AUTOR(ES)
Valderrama, B
RESUMO
In Rhizobium etli the nitrogenase reductase genes are reiterated. Strain CE3 has three copies; nifHa and nifHb form part of nifHDK operons with the nitrogenase structural genes, while nifHc is linked to a truncated nifD homolog. Their sequences are identical up to 6 residues upstream from a sigma54-dependent promoter. A remarkable difference among them is the absence of canonical NifA binding sites upstream of nifHc while a canonical binding site is located 200 bp upstream of nifHa and nifHb. To evaluate the transcriptional regulation of the reiterated nifH genes, we constructed fusions of nifHa and nifHc with the lacZ gene of Escherichia coli. Both genes were expressed at maximum levels under 1% oxygen in free-living cultures, and their expression declined as the oxygen concentration was increased. This expression was dependent on the integrity of nifA, and nifHc was expressed at higher levels than nifHa. The same pattern was observed with root nodule bacteroids. Expression of both genes in E. coli required sigma54 in addition to NifA bound to the upstream activator sequence. In vivo dimethyl sulfate footprinting analyses showed that NifA binds to the canonical site upstream of nifHa and to a TGT half-site 6 nucleotides further upstream. NifA protected an imperfect binding site upstream of nijHc at position 85 from the promoter. The integration host factor stimulated each gene differently, nifHa being more dependent on this protein. The above results correlate the asymmetric arrangement of cis-acting elements with a differential expression of the reiterated nifH genes, both in culture and during symbiosis with bean plants.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=178061Documentos Relacionados
- The regulatory VirG protein specifically binds to a cis-acting regulatory sequence involved in transcriptional activation of Agrobacterium tumefaciens virulence genes.
- Negative and positive cis-acting elements control the expression of murine alpha 1-protease inhibitor genes.
- cis-acting regulatory elements within gag genes of avian retroviruses.
- cis-acting regulatory elements involved in oxygen and light control of puc operon transcription in Rhodobacter sphaeroides.
- Localization of the cis-acting regulatory DNA sequences of the Myxococcus xanthus tps and ops genes.