The triphenylmethane dye, gallin, inhibits Escherichia coli RNA polymerase by 50% at a concentration of 8 µ. Gallin is a competitive inhibitor of DNA in the RNA polymerase reaction with a Ki of 3.5 µ the dye affects the apparent Km of GTP and ATP but not that of UTP and CTP. The apparent Km and Ki, expressed in micromolar concentrations are as follows: ATP, 80 and 16; GTP, 20 and 8.7; CTP, 8.5 and 20; UTP, 34 and 19. Measurement of γ-32P-labeled GTP and ATP incorporation into RNA indicates that low concentrations of gallin inhibit initiation of RNA chains but do not affect RNA chain elongation. The dye binds to RNA polymerase and, at low concentrations, inhibits association of the enzyme with its DNA template. These results suggest that gallin acts by binding to DNA-dependent RNA polymerase, thereby preventing attachment of DNA and the subsequent synthesis of RNA.
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