Fast, DNA-sequence independent translocation by FtsK in a single-molecule experiment

Escherichia coli FtsK is an essential cell division protein, which is thought to pump chromosomal DNA through the closing septum in an oriented manner by following DNA sequence polarity. Here, we perform single-molecule measurements of translocation by FtsK(50C), a derivative that functions as a DNA translocase in vitro. FtsK(50C) translocation follows Michaelis-Menten kinetics, with a maximum speed of similar to 6.7 kbp/s. We present results on the effect of applied force on the speed, distance translocated, and the mean times during and between protein activity. Surprisingly, we observe that FtsKsoc can spontaneously reverse its translocation direction on a fragment of E. coli chromosomal DNA, indicating that DNA sequence is not the sole determinant of translocation direction. We conclude that in vivo polarization of FtsK translocation could require the presence of cofactors; alternatively, we propose a model in which tension in the DNA directs FtsK translocation.