The effect of aurintricarboxylic acid on RNA polymerase from rat liver

The effect of the dye aurintricarboxylic acid (ATA) on RNA polymerases [EC 2.7.7.6] solubilized from rat liver was studied. Complete inhibition of RNA synthesis in vitro was observed when 3-5 microng/ml of ATA was added to the reaction mixture at time 0, while 40-70 microng/ml of a rifampicin derivative, AF/013, was required to produce the same extent of inhibition. RNA formation, however, continued at a rate of one-half that of the control when ATA was given after the onset of RNA synthesis in a dose capable of completely blocking RNA formation if administered at time 0. ATA was found to interact with RNA polymerizing enzyme itself and competed specifically with the binding of RNA polymerase to template DNA. Preincubation of the enzyme with DNA at 37 degrees before adding dye made the DNA-enzyme complex partly resistant to the drug. RNA-synthesizing activity resistant to ATA increased when nucleoside triphosphates, especially GTP, were added to the preincubation mixture in the presence of Mn2+. However, ATA only slightly affected RNA synthesis in nuclei isolated from rat liver.