We have investigated the mobility of two EGFP-tagged DNA repair proteins, WRN and BLM. In particular, we focused on the dynamics in two locations, the nucleoli and the nucleoplasm. We found that both WRN and BLM use a “DNA-scanning” mechanism, with rapid binding–unbinding to DNA resulting in effective diffusion. In the nucleoplasm WRN and BLM have effective diffusion coefficients of 1.62 and 1.34 μm2/s, respectively. Likewise, the dynamics in the nucleoli are also best described by effective diffusion, but with diffusion coefficients a factor of ten lower than in the nucleoplasm. From this large reduction in diffusion coefficient we were able to classify WRN and BLM as DNA damage scanners. In addition to WRN and BLM we also classified other DNA damage proteins and found they all fall into one of two categories. Either they are scanners, similar to WRN and BLM, with very low diffusion coefficients, suggesting a scanning mechanism, or they are almost freely diffusing, suggesting that they interact with DNA only after initiation of a DNA damage response.
DNA damage FRAP Diffusion DNA repair WRN BLM
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We would like to thank members of Center for Models of Life and the Bohr Laboratory for discussions. AT is supported by a Steno fellowship granted by the Danish Council for Independent research (DFF), KMB is supported by CMOL through the Danish National Research Foundation (DG), and MBJ is supported by the Center for Healthy Aging and an Elite Research Scholarship from the Danish Ministry of Science. This work was supported by funds from the intramural program of the National Institute of Aging, National Institutes of Health, USA.
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