Signal transduction cascade for regulation of RpoS: Temperature regulation of DsrA

Many environmental parameters modulate the amount of the RpoS sigma factor in Escherichia coli, Temperature control of RpoS depends on the untranslated RNA DsrA. DsrA activates RpoS translation by pairing with the Leader of the mRNA, We find that temperature affects both the rate of transcription initiation of the dsrA gene and the stability of DsrA RNA. Both are increased at low temperature (25 degreesC) compared to 37 or 42 degreesC, The combination of these results is 25-fold-Less DsrA at 37 degreesC and 30-fold Less at 42 degreesC than at 25 degreesC. Using an adapted lacZ-based reporter system, we show that temperature control of transcription initiation of dsrA requires only the minimal promoter of 36 bp. Overall, transcription responses to temperature lead to a sixfold increase in DsrA synthesis at 25 degreesC over that at 42 degreesC. Furthermore, two activating regions and a site for LeuO negative regulation were identified in the dsrA promoter, The activating regions also activate transcription in vitro. DsrA decays with a half-life of 23 min at 25 degreesC and 4 min at 37 and 42 degreesC, These results demonstrate that the dsrA promoter and the stability of DsrA RNA are the thermometers for RpoS temperature sensing. Multiple inputs to DsrA accumulation allow sensitive modulation of changes in the synthesis of the downstream targets of DsrA such as RpoS.