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 t he Escherichia coli growth cycle and the effect that mutation Delta cr p39 had on this expression were studied. The data obtained indicate th at the expression of gyrA is growth phase dependent and under the posi tive 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 backgrou nd 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 i nvolved in the modulation of DNA topology in the transition from the l ag period to the exponential phase of growth.