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Carlos Bustamente, Molecular & Cell Biology, Physics, and Chemistry, UC Berkeley
Sign posts along the chromosomal highway: How FtsK finds its target
DNA translocases are molecular motors that move rapidly along DNA using adenosine triphosphate as the source of energy. FtsK is a membrane-bound and septum-localized E. coli translocase that coordinates cell division with chromosome segregation. We directly observed the movement of purified FtsK, an Escherichia coli translocase, on single DNA molecules. The protein moves at 5 kilobases per second and against forces up to 60 piconewtons, and locally reverses direction without dissociation. On three natural substrates, independent of its initial binding position, FtsK efficiently translocates over long distances to the terminal region of the E. coli chromosome, as it does in vivo. Our results imply that FtsK is a bidirectional motor that changes direction in response to short, asymmetric directing DNA sequences. Moreover, single molecule observations together with an informatics analysis strongly suggest a particular octamer as the most likely FtsK Recognition Sequence or FRS. Direct testing of this sequence confirms its assignment. Finally, we have discovered that the FtsK domain is responsible for recognizing and reading the FRS.