Symbiotic autoregulation of nifA expression in Rhizobium leguminosarum bv. viciae

被引:16
作者
Martínez, M
Palacios, JM
Imperial, J
Ruiz-Argüeso, T
机构
[1] Univ Politecn Madrid, Dept Biotechnol, ETS Ingn Agron, E-28040 Madrid, Spain
[2] CSIC, E-28040 Madrid, Spain
关键词
D O I
10.1128/JB.186.19.6586-6594.2004
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
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 by from an upstream and divergent truncated duplication of nifH (DeltanifH). Symbiotic expression analysis of genomic nifA::lacZ fusions revealed that in strain UPM791 nifA is expressed mainly from a sigma(54)-dependent promoter (P-nifA1) located upstream of orf71. This promoter contains canonical NifA upstream activating sequences located 91 by from the transcription initiation site. The transcript initiated in P-nifA1 spans 5.1 kb and includes nifA and nifB genes. NifA from Klebsiella pneumoniae was able to activate transcription from P-nifA1 in a heterologous Escherichia coli system. In R. leguminosarum, the P-nifA1 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 P-nifA1 located immediately upstream of fixA.
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页码:6586 / 6594
页数:9
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