In vivo effect of DNA relaxation on the transcription of gene rpoH in Escherichia coli.

The in vivo effect of Novobiocin, a gyrase inhibitor, on the transcription of gene rpoH which codes for sigma32, the main positive regulator of the heat-shock response, was studied. Novobiocin induced a three-fold increase and a slight decrease in the activity of the rpoH promoters P1 and P4, respectively. The Novobiocin-induced increase in the activity of promoter P1 correlates with an increase in the amount of proteins sigma32 and DnaK. These results suggest that the increase in expression of the heat-shock proteins induced by gyrase inhibitors is probably due to the increased activity of P1 on relaxed DNA.