RFP reporter assay in E. coli . Each panel represents activation of a specific promoter by a specific RR as measured in RFUs (relative fluorescence units). RFUs were calculated as the ratio of RFP fluorescence to cell growth at OD590. Data shown are for 23 hours after start of assay. Error bars represent standard deviation. Grey columns represent negative controls where RFP fluorescence was measured in the absence of any RR (empty pETDEST42 vector). RR, response regulator.