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. 2014 May 31;42(12):7935–7946. doi: 10.1093/nar/gku494

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© The Author(s) 2014. Published by Oxford University Press on behalf of Nucleic Acids Research.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by-nc/3.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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Figure 6. — Residual supercoiling left unremoved by ScTopA relaxation bursts indicates ScTopA switches between high and low processivity as a function of torque acting on the DNA. Seventeen-kilobase DNA supercoiled by −50 turns and left to react with TopA shows (A) relaxation of ∼38 supercoils in the first 250 s of incubation but only (B) relaxation of ∼3 additional supercoils in the following 750 s of the reaction, for an extending force of about 0.3 pN. (Inset) When the extending force is increased to 1 pN, the average residual supercoiling is zero after a 250-s reaction. (C) Fifty-one-kilobase DNA supercoiled by −150 turns and left to react with TopA for 250 s shows an increase in residual supercoils roughly three times greater than what is observed on 17-kb DNA.