Figure 2.

Pausing at the his and ops pause sites. (A) Preformed [α-³²P]CMP-labeled A29 complexes were incubated with 10 μM GTP, 150 μM ATP, CTP, and UTP on the his (Left) or ops (Right) template. Samples were taken at the times indicated in seconds above each lane. Prominent transcripts (and lengths for his and ops templates, respectively) are P, pause RNA transcript (71 and 62 nt); T, terminated transcript (150 and 138 nt); and RO, run-off RNA transcript (381 and 369 nt). The fractions of the pause RNA (closed circles) were plotted against time; the pause half-life and efficiency were determined as described previously (24). Fractions of pause RNAs from preformed complexes (open squares; gels not shown) were determined after paused TECs were halted by NTP deprivation for ≈5 min.