Inhibition of DNA-dependent RNA polymerase with partially thiolated polynucleotides

Various modified polynucleotides, prepared from polycytidylic and polyuridylic acids as well as from RNA and DNA isolates by partial thiolation in the 5-position of their uracil and/or cytosine bases, strongly inhibited the DNA-dependent RNA polymerase of Micrococcus lysodeikticus. The inhibition was in the presence of mercaptoethanol partially reversible by the DNA template in a concentration-dependent manner, but was irreversible without the addition of mercaptoethanol. Incubation of the enzyme with the template prior to the addition of the inhibitor afforded some protection and decreased the inhibitory effects. The results suggest that the partially thiolated polynucleotides act by competing with the DNA template for the "template site" of the enzyme. In the absence of mercaptoethanol, covalent binding via mixed disulfide linkages may take place between the inhibitor and the enzyme.