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. 2017 Mar 27;26(7):1427–1438. doi: 10.1002/pro.3156

Figure 4.

Figure 4

LacI bound to an O1 operator pauses transcription. (A) A schematic representation of the DNA template used in magnetic tweezer transcription assays. The template contained a T7A1 promoter close to the upstream end, a stall site at position +22, an O1 operator, the lambda t1 terminator (λt1) and a biotin label at the downstream end. A streptavidin‐labeled paramagnetic bead was coupled to the biotin label to for micromanipulation in the magnetic tweezer. Four examples of transcriptional elongation recorded using the magnetic tweezers are displayed. In (B) no LacI was included and transcription shortened the DNA tether progressively without interruption. When LacI was included (C–E), transcription shortened the tether by about 0.2 um before pausing for about 200 s and then resuming. Transcription finally ceased after the tether shortened by either 0.35 um (C and D), a distance corresponding to the location of a terminator sequence, or 0.5 um (B and E), a distance corresponding to the end of the template.