Regulation of the cnr cobalt and nickel resistance determinant from Ralstonia sp strain CH34

Ralstonia sp. strain CH34 is resistant to nickel and cobalt cations. Resist ance is mediated by the cnr determinant located on plasmid pMOL28. The cnr genes are organized in two clusters, cnrYXH and cnrCBA. As revealed by reve rse transcriptase PCR and primer extension, transcription from these operon s is initiated from promoters located upstream of the cnrY and cnrC genes. These two promoters exhibit conserved sequences at the -10 (CCGTATA) and -3 5 (CRAGGGGRAG) regions. The CnrH gene product, which is required for expres sion of both operons, is a sigma factor belonging to the sigma L family, wh ose activity seems to be governed by the membrane-bound CnrY and CnrX gene products in response to Ni2+. Half-maximal activation from the cnrCBA opero n was determined by using appropriate lacZ gene fusions and was shown to oc cur at an Ni2+ concentration of about 50 mu M.