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Biological Chemistry

Tracking DNA Repair In Live Bacteria

Fluorescence microscopy methods measure processes at single-molecule and single-cell levels

by Celia Henry Arnaud
May 6, 2013 | A version of this story appeared in Volume 91, Issue 18

Researchers have combined two single-molecule methods to take a quantitative look at DNA repair in live bacteria. Antoine van Oijen, a biophysicist at the University of Groningen, in the Netherlands, who was not involved in the work, calls the report “a fantastic example of how single-molecule and single-cell methods allow the study of biological problems at a level of quantification that hitherto was unthinkable.” Stephan Uphoff and Achillefs N. Kapanidis of the University of Oxford and coworkers used photoactivated localization microscopy and single-molecule tracking to watch the enzymes DNA polymerase I and ligase while they repaired damaged DNA in single Escherichia coli cells (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1301804110). With a single set of measurements, the researchers were able to determine multiple characteristics of the process at the single-cell level. Each cell had on average approximately 480 copies of polymerase I and 230 copies of ligase. Repair sites were spread throughout the cell. The researchers found that individual repair events take 2.1 seconds for polymerase I and 2.5 seconds for ligase, and the enzymes spend more than 80% of the time looking for substrates.

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