Salmonella typhimurium DsbA is growth-phase regulated

Northern blot analyses, transcription assays using a dsbA::lacZ transcriptional fusion, and primer extension mapping were used to characterize the promoter region of dsbA from Salmonella typhimurium. Transcription assays measuring promoter activity of a 258-bp segment of DNA immediately upstream of the dsbA translational start site showed strong growth-phase dependence, with maximal expression in stationary phase and high levels of expression maintained for at least 72 h. This expression was not RpoS-dependent. Two transcripts initiating in the dsbA promoter region were mapped by primer extension analysis and their levels were monitored by Northern blot analysis. Growth conditions such as pH and O(2) levels affected dsbA transcription independently of growth phase. The data suggests that the promoter region of S. typhimurium is not constitutively activated. Its regulation may reflect a requirement for DsbA during conditions resulting in stationary-phase-like growth in the environment.