Fig. 8.

Determination of the torque generated by RNAP during transcription. a A drawing depicting the “twin-supercoiled-domain” model and experimental configuration to measure transcription against (−) supercoiling upstream (behind the RNAP) or (+) supercoiling downstream (in front of the RNAP). Escherichia coli RNAP was torsionally anchored to the surface of a coverglass while either the downstream end or upstream end of the DNA template was torsionally constrained to a quartz cylinder held in an AOT. The AOT monitored the translocation of the RNAP along DNA and the torque generated by RNAP in real-time. RNAP elongation accumulated (+) or (−) DNA supercoiling, respectively. As torque increased, RNAP was eventually stalled and the AOT reported the value of the stall torque. b Distributions of the measured downstream (left) and upstream (right) stall torques of RNAP. Adapted from Ma et al. (2013) with permission