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Journal of Bacteriology, October 2004, p. 6586-6594, Vol. 186, No. 19
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.19.6586-6594.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Symbiotic Autoregulation of nifA Expression in Rhizobium leguminosarum bv. viciae

Marta Martínez,1 José M. Palacios,1 Juan Imperial,2 and Tomás Ruiz-Argüeso1*

Departamento de Biotecnología, E. T. S. Ingenieros Agrónomos, Universidad Politécnica de Madrid,1 Consejo Superior de Investigaciones Científicas, Madrid, Spain2

Received 10 March 2004/ Accepted 14 June 2004

NifA is the general transcriptional activator of nitrogen fixation genes in diazotrophic bacteria. In Rhizobium leguminosarum bv. viciae UPM791, the nifA gene is part of a gene cluster (orf71 orf79 fixW orf5 fixABCX nifAB) separated by 896 bp from an upstream and divergent truncated duplication of nifH ({Delta}nifH). Symbiotic expression analysis of genomic nifA::lacZ fusions revealed that in strain UPM791 nifA is expressed mainly from a {sigma}54-dependent promoter (PnifA1) located upstream of orf71. This promoter contains canonical NifA upstream activating sequences located 91 bp from the transcription initiation site. The transcript initiated in PnifA1 spans 5.1 kb and includes nifA and nifB genes. NifA from Klebsiella pneumoniae was able to activate transcription from PnifA1 in a heterologous Escherichia coli system. In R. leguminosarum, the PnifA1 promoter is essential for effective nitrogen fixation in symbiosis with peas. In its absence, partially efficient nitrogen-fixing nodules were produced, and the corresponding bacteroids exhibited only low levels of nifA gene expression. The basal level of nifA expression resulted from a promoter activity originating upstream of the fixX-nifA intergenic region and probably from an incomplete duplication of PnifA1 located immediately upstream of fixA.

* Corresponding author. Mailing address: Departamento de Biotecnología, E. T. S. de Ingenieros Agrónomos, Ciudad Universitaria s/n, 28040 Madrid, Spain. Phone: 34-913365759. Fax: 34-913365757. E-mail: ruizargueso{at}bit.etsia.upm.es.

Journal of Bacteriology, October 2004, p. 6586-6594, Vol. 186, No. 19
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.19.6586-6594.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Martinez, M., Colombo, M.-V., Palacios, J.-M., Imperial, J., Ruiz-Argueso, T. (2008). Novel Arrangement of Enhancer Sequences for NifA-Dependent Activation of the Hydrogenase Gene Promoter in Rhizobium leguminosarum bv. viciae. J. Bacteriol. 190: 3185-3191 [Abstract] [Full Text]  
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