De. Mathews et Rd. Durbin, MECHANISTIC ASPECTS OF TAGETITOXIN INHIBITION OF RNA-POLYMERASE FROM ESCHERICHIA-COLI, Biochemistry, 33(39), 1994, pp. 11987-11992
Tagetitoxin inhibits RNA synthesis directed by bacterial RNA polymeras
e, 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 dur
ing elongation of a nascent RNA chain. In abortive initiation assays,
the rate of dinucleotide formation is inhibited by tagetitoxin when in
itiated with ATP or CpA but not when AMP is used to initiate. Formatio
n of longer oligonucleotides is inhibited by the toxin regardless of t
he initiating nucleotide. These abortive initiation studies indicate t
hat tagetitoxin does not affect nucleotide substrate binding or phosph
odiester bond formation and suggest that the toxin may interfere with
a subsequent step. It is suggested that tagetitoxin affects the stabil
ity of nascent oligonucleotide binding and/or the translocation of the
catalytic center with respect to the 3'-OH of nascent oligonucleotide
s.