Regulation of the cnr Cobalt and Nickel Resistance Determinant from Ralstonia sp. Strain CH34

Abstract

Ralstonia sp. strain CH34 is resistant to nickel and cobalt cations. Resistance is mediated by the cnrdeterminant located on plasmid pMOL28. The cnr genes are organized in two clusters, cnrYXH and cnrCBA. As revealed by reverse transcriptase PCR and primer extension, transcription from these operons is initiated from promoters located upstream of the cnrY and cnrC genes. These two promoters exhibit conserved sequences at the −10 (CCGTATA) and −35 (CRAGGGGRAG) regions. The CnrH gene product, which is required for expression of both operons, is a sigma factor belonging to the sigma L family, whose activity seems to be governed by the membrane-bound CnrY and CnrX gene products in response to Ni²⁺. Half-maximal activation from the cnrCBAoperon was determined by using appropriate lacZ gene fusions and was shown to occur at an Ni²⁺ concentration of about 50 μM.