title: Partial characterization of the mode of inhibition of Escherichia coli RNA polymerase by the mixed disulfide, CoASSG.
abstract: 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.
mesh_terms: D003065:Coenzyme A / Q000031:analogs & derivatives* / Q000494:pharmacology; D012321:DNA-Directed RNA Polymerases / Q000037:antagonists & inhibitors*; D004926:Escherichia coli / Q000201:enzymology*; D005978:Glutathione / Q000031:analogs & derivatives* / Q000494:pharmacology; D007501:Iron / Q000494:pharmacology; D007700:Kinetics; D012293:Rifampin / Q000494:pharmacology; D013329:Structure-Activity Relationship; D013698:Templates, Genetic; D014158:Transcription, Genetic
chemical_list: C019305:coenzyme A-glutathione mixed disulfide; D007501:Iron; D012321:DNA-Directed RNA Polymerases; D005978:Glutathione; D003065:Coenzyme A; D012293:Rifampin