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Measurement of the torque in braided DNAs using a thermodynamic Maxwell relation

By Botao Xiao, Sumitabha Brahmachari, Yang Liu, Ke Ding, John F. Marko

Posted 07 Feb 2020
bioRxiv DOI: 10.1101/2020.02.07.938209

Braided DNAs are significant structural intermediates in cellular processes, yet little has been experimentally demonstrated about their higher-order structure and twisting torques. We use magnetic tweezers to measure braid extensions at forces ranging from 0.3 to 8 piconewtons, and then apply a thermodynamic Maxwell relation to calculate the torque. Experimentally inferred torques in unbuckled braids take on values up to 76 pNnm, which depends on force, and inter-tether distance. As predicted using a statistical mechanical model, the twist modulus of the braids increases with catenation prior to buckling or formation of plectoneme, and is comparable to that of single DNA.

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