Cyclic AMP receptor protein positively controls gyrA transcription and alters DNA topology after nutritional upshift in Escherichia coli.

The expression of a transcriptional gyrA-lacZ gene fusion throughout the Escherichia coli growth cycle and the effect that mutation delta crp39 had on this expression were studied. The data obtained indicate that the expression of gyrA is growth phase dependent and under the positive control of the cyclic AMP receptor protein (CRP). Complementation analysis of gyrA-lacZ expression with wild-type CRP or variant CRP pc (with a T-to-A mutation at position 158) in a CRP-deficient background suggests that this CRP action is mediated by a class I or class II CRP-dependent promoter(s). Our results also indicate that CRP may be involved in the modulation of DNA topology in the transition from the lag period to the exponential phase of growth.