Partial characterization of the mode of inhibition of Escherichia coli RNA polymerase by the mixed disulfide, CoASSG

The coenzyme A – glutathione mixed disulfide (CoASSG), when complexed with iron, is capable of inhibiting the RNA polymerase of Escherichia coli. A modified procedure involving a short time of exposure to high salt allowed the reliable preparation of CoASSG–Fe which was active in inhibiting RNA polymerase. The CoASSG–Fe complex acted as a noncompetitive inhibitor for the incorporation of all four nucleoside triphosphates but had a greater effect on GMP and CMP incorporation than AMP and UMP incorporation. Neither temperature nor ionic-strength changes affected CoASSG–Fe inhibition, and the use of rifampicin showed that CoASSG–Fe did not inhibit either the initiation or elongation processes of the polymerase. CoASSG–Fe was a more effective inhibitor at low DNA-template concentrations and it was more effective in inhibiting the incorporation of CMP and GMP on simple dG-dC containing templates and the asymmetric polymer poly d(T-C)∙poly d(G-A). The inhibition of transcription of poly d(I-C) was less effective than the inhibition of transcription of poly d(G-C). Equilibrium dialysis in microdialysis cells showed that CoASSG–Fe could associate with DNA in the absence of RNA polymerase.