Torque in Stretched and Twisted DNA

Tuesday, September 18, 2007 - 1:30pm - 2:30pm
EE/CS 3-180
John Marko (Northwestern University)
In experiments where DNA is pulled at constant force and twisted, a mixed
state of extended twisted DNA and plectonemically supercoiled DNA is
easily obtained. I will review the thermodynamics of this state
coexistence phenomenon. A particularly elegant use of
plectoneme-extended DNA coexistence is as a source of constant torque for
single-DNA experiments. I will discuss the estimation of torques and free
energies in such experiments, and I will provide some useful closed-form
formulae, most notably for the torque in DNA as a function of force. I
will review experiments where estimation of DNA torques allowed study of
rotational friction during DNA relaxation by type IB and IC
topoisomerases. I will also discuss experiments where DNA torques were
directly measured rather than estimated.

Reference: J.F. Marko, Torque and dynamics of linking number relaxation
in stretched supercoiled DNA, Phys. Rev. E 76, Art. 021926 (2007)
MSC Code: