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EMBO Rep. 2013 May;14(5):473-9. doi: 10.1038/embor.2013.39. Epub 2013 Apr 5.

SpoIIIE mechanism of directional translocation involves target search coupled to sequence-dependent motor stimulation.

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Centre de Biochimie Structurale, CNRS UMR5048, INSERM U1054, Université de Montpellier I & II, 34090 Montpellier, France.


SpoIIIE/FtsK are membrane-anchored, ATP-fuelled, directional motors responsible for chromosomal segregation in bacteria. Directionality in these motors is governed by interactions between specialized sequence-recognition modules (SpoIIIE-γ/FtsK-γ) and highly skewed chromosomal sequences (SRS/KOPS). Using a new combination of ensemble and single-molecule methods, we dissect the series of steps required for SRS localization and motor activation. First, we demonstrate that SpoIIIE/DNA association kinetics are sequence independent, with binding specificity being uniquely determined by dissociation. Next, we show by single-molecule and modelling methods that hexameric SpoIIIE binds DNA non-specifically and finds SRS by an ATP-independent target search mechanism, with ensuing oligomerization and binding of SpoIIIE-γ to SRS triggering motor stimulation. Finally, we propose a new model that provides an entirely new interpretation of previous observations for the origin of SRS/KOPS-directed translocation by SpoIIIE/FtsK.

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