Direct observation of DNA rotation during transcription by Escherichia coli RNA polymerase

Helical filaments driven by linear molecular motors are anticipated to rota te around their axis, but rotation consistent with the helical pitch has no t been observed. 14S dynein(1) and non-claret disjunctional protein (ncd)(2 ) rotated a microtubule more efficiently than expected for its helical pitc h, and myosin rotated an actin filament only poorly(3). For DNA-based motor s such as RNA polymerase, transcription-induced supercoiling of DNA(4) supp orts the general picture of tracking along the DNA helix(5). Here we report direct and real-time optical microscopy measurements of rotation rate that are consistent with high-fidelity tracking. Single RNA polymerase molecule s attached to a glass surface rotated DNA for >100 revolutions around the r ight-handed screw axis of the double helix with a rotary torque of >5 pN nm . This real-time observation of rotation opens the possibility of resolving individual transcription steps.