Two genes encoding a putative multidrug efflux pump of the RND/MFP family are cotranscribed with an rpoH gene in Bradyrhizobium japonicum.
The rpoH3 gene of Bradyrhizobium japonicum codes for one of three sigma32-type transcription factors in this organism and is flanked by rag (rpoH3-associated) genes comprising the chromosomal arrangement ragABrpoH3ragCD. The first genes in this cluster code for a classical two-component regulatory system with an unknown function (Narberhaus et al., 1997. Mol. Microbiol. 24, 93-104). The deduced proteins of the last two genes display a high sequence similarity to heavy metal or multidrug efflux pumps of the RND (Resistance/Nodulation/cell Division)-MFP (Membrane Fusion Protein) family. Reverse transcription and polymerase chain reaction (RT-PCR) analysis demonstrated that ragC is cotranscribed with rpoH3. Mutant strains carrying disrupted rag genes or an extented deletion of the rag locus exhibited neither an apparent growth defect nor a deficiency in the symbiotic interaction with soybean roots. The minimal inhibitory concentrations (MICs) of various metals and organic compounds were identical for the wild-type and mutant strains. Moreover, translational lacZ fusions to each of the first four genes of the rag cluster showed a very low expression under all conditions tested; hence, the substrate for the putative efflux pump has not been uncovered.
Krummenacher
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P
Institut für Mikrobiologie, Eidgenössische Technische Hochschule, Zürich, Switzerland.
Narberhaus
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D001426:Bacterial Proteins / Q000235:genetics*; D020369:Bradyrhizobium / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping; D015870:Gene Expression; D005798:Genes, Bacterial; D008565:Membrane Proteins / Q000235:genetics*; D005810:Multigene Family; D009154:Mutation; D010641:Phenotype; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D008565:Membrane Proteins; C106852:RpoH3 protein, Bradyrhizobium japonicum; D014157:Transcription Factors