Inhibition of DNA-dependent RNA synthesis by rifamycins.

Fig. 1. Effect of rifamycins on RNA polymerase reactions of E. coli and Ehrlich carcinoma cells. The reaction mixture for the assay of E. coli RNA polymerase contained (0.3 ml) Tris-HCl, pH 8.0, 15 //moles; /?-mercaptoethanol, 3.6 //moles; MgCl2, 1.2 //moles; MnCl2, 0.3 //moles; ATP, GTP and UTP, 0.1 //mole each; 3H-CTP, 0.05 //moles (3,000 cpm/m/zmole); calf thymus DNA, 30 jug, enzyme, 20jug. Incubation was at 37°C for 10 minutes. The mixture for the assay of Ehrlich cell RNA polymerase contained (0.3 ml) Tris-HCl, pH 7.8, 15 //moles; j9-mercaptoethanol, 3 //moles; MgCl2, 2.4 //moles; MnCl2, 0.6 //mole; ATP, GTP and UTP, 0.1 //mole each; ^H-CTP, 0.012 //mole (30,000 cpm/m/zmole) ; calf thymus DNA, 25 jug; enzyme, 0.34 mg. Incubation was at 37°C for 20 minutes. /Op l/OO whether rifamycins have the same mode of action on DNA-dependent RNA synthesis of E. coli because of their structural resem blance4^ In this communication, we report the mode of action of rifamycin B and rifamycin SV on DNA-dependent RNA polymerase reac tions of both E. coli and Ehrlich ascites carcinoma cells. DNA-dependent RNA polymerase from E. coli B was prepared by the method of Chamberlin and Berg5) and that from Ehrlich ascites cells was extracted as reported pre viously^. The procedure for the assay of RNA polymerase was the same as described in a previous paper2). Rif mycin B and rifamycin SV were kindly given by Dr. P. Sensi, Research La boratories, Lepetit, S.p.A., Milan, Italy. Fig. 1 shows the effect of rifamycin B and rifamycin SV on DNA-dependent RNA poly merase reactions of E. coli and of Ehrlich ascites carcinoma cells. The results indicate that the incorporation of 3H-CMP into acid insoluble fraction by RNA polymerase of E. coli was markedly inhibited by both anti biotics at a concentration as low as 0.1 jum. However, the 3H-CMP incorporation by RNA polymerase of Ehrlich ascites carci