Fig. 2.

Low rate of UTP incorporation compared to the other NTPs in vitro is consistent with RNAP pausing upstream of +1T in vivo. (A) +1T is the only conserved residue in the sequence logo of pause peaks shared by WT and ΔnusG strains. (B) Transcription was performed using a TTT-to-CAA mutant ribD template that eliminates pausing (see below). Where indicated, one NTP was held at a limiting concentration (10 µM), while the other three NTPs were at 150 µM. Time points of elongation were 15, 20, 30, 40, 55, 70, 90, 120, and 160 s. Positions of terminated (T) and run-off (R) transcripts are indicated.