Downregulation of the Escherichia coli guaB promoter by FIS

The Escherichia coli guaB promoter (P(guaB)) regulates transcription of two genes, guaB and guaA, that are required for the synthesis of guanosine 5'-monophosphate (GMP), a precursor for the synthesis of guanine nucleoside triphosphates. Transcription from P(guaB) increases as a function of increasing cellular growth rate, and this is referred to as growth rate-dependent control (GRDC). Here we investigated the role of the factor for inversion stimulation (FIS) in the regulation of this promoter. The results showed that there are three binding sites for FIS centred near positions -11, +8 and +29 relative to the guaB transcription start site. Binding of FIS to these sites results in repression of P(guaB) in vitro but not in vivo. Deletion of the fis gene results in increased P(guaB) activity in vivo, but GRDC of P(guaB) is maintained.