Precise excision of Tn5 in Escherichia coli K12 mutants with alterations in common component of phosphotransferase system and in DNA-gyrase subunits

Abstract

The effect of ptsH, gyrA and gyrB mutations on the frequency of 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 the experiments. It was shown that mutational damage to the HPr protein (ptsH mutation), a common component of the bacterial PEP-dependent phosphotransferase system (PTS), or changes in the DNA-gyrase A subunit (gyrA mutation) increased the frequency of PE. The gyrB mutation (mutational damage of DNA-gyrase B subunit) had almost no influence on PE frequency. The presence of glucose or fructose in growth media resulted in enhanced PE frequency, while the insertion of ptsH or gyrA mutations under the same conditions caused a decrease in the PE frequency. gyrB mutants had no similar effects. The demonstrated data indicate the need for the intact PTS for the balanced supercoiled DNA state maintained by DNA gyrase.