FIG 3.

Impact of ArmZ on MexZ binding to mexXYp in vitro and in vivo in the heterologous host E. coli. (A) EMSA of MexZ-His₆ and His₆-ArmZ binding to a 184-bp mexXYp DNA fragment. DNA at a concentration of 0.1 μM was incubated with the indicated concentrations of MexZ-His₆, His₆-ArmZ, or both proteins; separated on a 1.5% agarose gel; stained with ethidium bromide; and photographed. A 204-bp pUC19 fragment (amplified using primers 46 and 7) was used to verify the specificity of MexZ binding. (B) MexZ repression of mexXYp in a heterologous host. XylE activity measurements were performed with cell extracts from cultures of E. coli DH5α strains containing the indicated plasmids grown in medium with different concentrations of arabinose, to overproduce MexZ (pKAB801 araBADp-mexZ). Data are presented on a semilogarithmic plot. (C) Effect of ArmZ or ArmZ/PA5470 overproduction on MexZ repression of mexXYp in E. coli DH5α. XylE activity was assayed in extracts of E. coli DH5α transformants grown in the presence of two inducers, IPTG and arabinose. Data represent mean activities from at least three cultures ± SD.