Tagetitoxin inhibition of RNA polymerase III transcription results from enhanced pausing at discrete sites and is template-dependent.

In yeast nuclear extracts, tagetitoxin inhibition of RNA polymerase III promoter-directed single- and multiple-round transcription is characterized by pausing or stalling of the elongation complex at several discrete points on the template. Paused ternary complexes isolated from tagetitoxin-inhibited reactions can be elongated to produce full-length RNA. The distribution of "tagetitoxin-enhanced" pause sites is distinct for each of the class III genes we have examined. These tagetitoxin-enhanced pause sites may also be intrinsic pause sites for the elongation complex. Tagetitoxin inhibition of in vitro transcription of the yeast SUP4 and SUP6 tRNA(Tyr) genes demonstrates template dependence and indicates that inhibition may occur after UMP incorporation. Factor-independent transcription by purified yeast RNA polymerase III can also be inhibited by tagetitoxin, and the degree of inhibition is template-dependent. Tagetitoxin may be most effective as an inhibitor under conditions where polymerase III tends to pause on the template. We propose that differences in tagetitoxin inhibition among class III genes may reflect differences in the number of stability of these pause sites.