Scientists have used an optical trap to track the movement of RNA polymerase (RNAP), showing that the enzyme appears to shift along DNA one base pair at a time. Although many experts had expected this conclusion, the report, appearing in this week's Nature, reports the motion at a scale ten times finer than previous work, allowing the researchers to directly resolve the individual steps. This angstrom-scale resolution could shed light on less-understood aspects of gene transcription and its regulation, as well as on the tiny motions of other enzymes as they perform their chemical tasks.

The researchers, led by Steven Block of Stanford University, Ca., improved the stability of their optical trap so that it could resolve single-base-pair steps of E. coli RNAP in solution. In this way they were able to recognize and eliminate occasional pauses and backtracking, isolating the "bare" elongation rate. They confirmed that the...

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