Transient pausing by RNA polymerase II

Price comments on a study that questions RNA polymerase II (Pol II) elongation control utilized during transcription of most metazoan genes. Researchers generated a human cell line solely expressing GFP-tagged Pol II and then used fluorescence recovery after photobleaching (FRAP) to identify and characterize four distinguishable kinetic states for Pol II. Besides the very rapid recovery due to diffusion of free Pol II, they found three bound states, each with about an order of magnitude slower recovery than the preceding one. These kinetic states were assigned to initiation, pausing, and productive elongation by observing how well-characterized compounds affected the FRAP measurements.