Figure 4.

Assaying for intrinsic transcript termination at rrnBT1 on ssDNA. C₄₇ complexes bound to Ni²⁺-NTA agarose in TGK-B₄₀M₄ were chased with 500 μM ATP, 500 μM GTP, 500 μM CTP, and 500 μM UTP for 10 min at 37°C in the presence of rifampicin at 20 μg/ml and yeast Torula RNA at 0.8 mg/ml. The lanes are assigned as for Fig. 2A. The rrnBT1 terminator is at positions +132, +133, and +134, whereas transcription to the end of the DNA template generates a run-off RNA of 205 nucleotides. C₄₇ complexes in lanes 5–8 were digested with Exo III at 5,000 units/ml for 5 min at 37°C.