Mechanistic aspects of tagetitoxin inhibition of RNA polymerase from Escherichia coli.

Tagetitoxin inhibits RNA synthesis directed by bacterial RNA polymerase, and the current study explores several mechanistic aspects of this inhibition. Tagetitoxin inhibition of in vitro RNA synthesis directed by Escherichia coli RNA polymerase is independent of the template DNA concentration. The toxin can block Escherichia coli RNA polymerase during elongation of a nascent RNA chain. In abortive initiation assays, the rate of dinucleotide formation is inhibited by tagetitoxin when initiated with ATP or CpA but not when AMP is used to initiate. Formation of longer oligonucleotides is inhibited by the toxin regardless of the initiating nucleotide. These abortive initiation studies indicate that tagetitoxin does not affect nucleotide substrate binding or phosphodiester bond formation and suggest that the toxin may interfere with a subsequent step. It is suggested that tagetitoxin affects the stability of nascent oligonucleotide binding and/or the translocation of the catalytic center with respect to the 3'-OH of nascent oligonucleotides.