DNA-dependent RNA polymerase from Enterobacter cloacae is closely related to Escherichia coli

The RNA polymerase holoenzyme (RNAP) of Enterobacter cloacae was purified by gel filtration and heparin affinity chromatography and shown to consist of four subunits (beta', beta, alpha and sigma) of 156, 151, 45 and 82 kDa, as measured by SDS-PAGE. The 82 kDa protein was shown to be related to the Escherichia coli primary sigma factor by western blot analysis with polyclonal antisera raised against purified E. coli sigma 70. Functional reconstitution of E. cloacae core enzyme with purified E. coli sigma 70 showed that E. cloacae and E. coli sigma factors are closely related. The RNAP of E. cloacae initiated transcription from the tac promoter with an efficiency similar to that of E. coli. Measuring promoter-specific transcription, the dependence of holoenzyme activity on salt, divalent cation and temperature was also similar to that of the E. coli RNAP. We also showed that the transcriptional inhibitor, rifampicin, inhibits the enzyme activity of the purified RNAP of E. cloacae and E. coli at similar concentrations. We conclude, based on these data, that the RNAP of E. cloacae and E. coli, both enterobacteria, are closely related.