Figure 7.

Slowing the rate of transcript release does not allow rho to act on pol I. The transcription template described in Fig. 1 was further modified by substituting the binding site for lac repressor for the Reb1 site. Repressor was positioned to pause pol I exactly where Reb1 would pause it (18). Templates were transcribed by either pol II (lanes 1–8) or pol I (lanes 9–19) for 30 min and then separated into bound or released fractions. Rho was present throughout the reaction in lanes 3, 4, 7, 8, 11, 12, 15, and 16. The orientation of the RUT site on the template was altered as indicated below the figure. Asterisks indicate transcripts that differ in length by 30 nucleotides and presumably represent ternary complexes stacked up behind lac repressor. Note that all reactions in this figure were run under identical ionic conditions (i.e., glutamate).