Abstract
In the cell, nucleic acid motor proteins act on substrates occupied by other proteins, yet little is known regarding the inevitable collisions that must occur. Using nanofabricated curtains of DNA and real-time, multi-color single-molecule microscopy we visualized collisions between two model translocases and DNA-bound obstacles. We show that both RecBCD, a helicase necessary for initiating homologous DNA recombination, and FtsK, a DNA pump involved in chromosome dimer resolution, actively disrupts nucleoprotein complexes, including RNA polymerase (RNAP) holoenzyme. RecBCD pushed and eventually displaces RNAP, Lac repressor, EcoRI(E111Q) and even nucleosomes. FtsK pushed RNAP but was able to either push or bypass EcoRI(E111Q). We conclude that RecBCD acts as a powerful stripase that overwhelms potential roadblocks. In contrast, FtsK is able to bypass some roadblocks, possibly by dissociation and reassembly ahead of the block.
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