The effect of ptsH and gyrA mutations on precise excision (PE) of transposon Tn5 was studied in Escherichia coli K12. The conjugative plasmid with Tn5 integrated in the tet gene of Tn10 was used as a model in experiments. It was shown that mutational damage of HPr, a common component of the bacterial PEP-dependent phosphotransferase system (PTS), increased the frequency of PE. The alteration of the subunit A of DNA-gyrase (gyrA mutation) was found to enhance the frequency of PE. The ptsH mutation had the same effect. Mutational damage of the DNA-gyrase subunit B (gyrB mutation) had no effect on the frequency of PE. The data reported in this work are evidence of the necessity of the intact PTS for the balanced supercoiled DNA state maintained by DNA-gyrase.