We hypothesized that the PhoP-activated yrbL gene of Escherichia coli might participate in an analogous loop with the PmrA protein because both the Salmonella pmrD and Escherichia coli yrbL promoters can be found in the same promoter profile and harbor similarly arranged PhoP and PmrA boxes ( Fig. 1 D and E ) .
A possible multicomponent loop involving the PhoP-activated yrbL gene .
As shown in Fig. 4C , this motif is also observed in a similar position and in the same orientation in a subset of PhoP-activated genes , including phoP , mgtA , pmrD , yrbL , slyB , and orgB ( 49 ) .