Can you access this paper?
It might be of some use:
http://www.sciencedirect.com/science/article/pii/0012160679900186
and this is cool:
http://www.sciencemag.org/content/287/5462/2497.short
Quotes from Davenport, Wuite, Landick, Bustamante (2000) (the above link):
"A stalled [RNA pol + DNA] complex is tethered between two... beads and kept in a continuous buffer flow." One bead is held in place by a pipette, and the RNA pol is attached to this bead, the other bead is attached to the other end of the DNA molecule, so essentially imagine a DNA molecule with a bead at either end, the RNA pol, attached to the anchored (by the pipette) bead, is stalled along the DNA molecule. Once started, "[a]s a transcribing polymerase moves along the DNA, it physically pulls the two beads closer together. The separation of the beads was measured by video microscopy and used to determine the end-to-end distance and the contour length of the DNA". Then "a time derivative was taken to obtain the transcription rate"; essentially, the speed with which the beads move togeather was used to detemrine the transcription rate.
This is my understanding, at least. If one of the more knowleadgable members can correct me if I am wrong, please do.
