RNA polymerase on the clock

Is RNA polymerase II slacking off while it's supposed to be on the job? Probably not. But as Boireau et al. report, the first measurements of RNA kinetics in individual cells show an unaccounted for two and a half minutes in the protein's schedule.

Using groups of cells, researchers have previously determined averages for how many nucleotides RNA polymerase II can add in a minute (900–1,800), its initiation rate, and other variables. To refine these figures, Boireau et al. gauged how fast single cells transcribe a segment of the HIV genome. The researchers altered the segment to contain multiple binding sites for the protein MS2. By adding GFP-labeled MS2, which binds to the transcript, the researchers could track the growth of the new RNA strand. Mathematical models then allowed the team...