Two-subunit DNA escort mechanism and inactive subunit bypass in an ultra-fast ring ATPase
SpoIIIE is a homo-hexameric dsDNA translocase responsible for completing chromosome segregation in B. subtilis. Here we use a single-molecule approach to monitor SpoIIIE translocation when challenged with neutral-backbone DNA and non-hydrolyzable ATP analogs. We show that SpoIIIE makes multiple essential contacts with phosphates on the 5'→3' strand in the direction of translocation. Using DNA constructs with two neutral-backbone segments separated by a single charged base-pair, we deduce that SpoIIIE's step size is 2 bp. Finally, experiments with non-hydrolyzable ATP analogs suggest that SpoIIIE can operate with non-consecutive inactive subunits. We propose a two-subunit escort translocation mechanism that is strict enough to enable SpoIIIE to track one DNA strand, yet sufficiently compliant to permit the motor to bypass inactive subunits without arrest. We speculate that such flexible mechanism arose for motors that, like SpoIIIE, constitute functional bottlenecks where the inactivation of even a single motor can be lethal for the cell.
Article and author information
- Taekjip Ha, Johns Hopkins University School of Medicine
- Received: June 4, 2015
- Accepted: October 8, 2015
- Accepted Manuscript published: October 9, 2015 (version 1)
- Accepted Manuscript updated: October 14, 2015 (version 2)
- Version of Record published: December 23, 2015 (version 3)
© 2015, Liu et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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