Figure 2. Dual-beam optical trapping assays can be used to monitor RNAP II transcription. In the example shown, an elongating RNAP II and a molecule of DNA are individually attached to beads, which are held in separate optical traps. The system can be used to impart hindering or assisting force on the polymerase during transcription to produce an RNA (in red). The position of RNAP II along the template can be monitored as a function of time to understand the duration and density of pausing events. The figure is adapted from Michaelis and Treutlein.³⁵