Both in vivo and in vitro, specific sequences in double-stranded DNA can adopt the left-handed Z-form when underwound. Recently, the B-Z transition of DNA has been studied in detail in magnetic tweezers experiments by several groups. We present a theoretical description of this transition, based on an annealed random copolymer model. The transition of a switchable sequence is discussed as a function of energetic and geometric parameters of the B- and Z-forms, of the applied boundary conditions, and of the characteristics of the B-Z interface. We address a possible torsional softening upon the B-Z transition. The model can be also applied to other biofilaments with annealed torsional/flexural degrees of freedom.
Bibliographical noteFunding Information:
N.-K.L. acknowledges financial support from the Korean Research Foundation via grants No. 2012R1A1A3013044 and No. 2014R1A1A2055681. N.-K.L. and A.J. acknowledge support from the Star Exchange Program (grant No. NRF-2012K1A3A1A21030441). This work is also supported by Korean Research Foundation grant No. 2012R1A1A2021736 (to S.-C.H.).
© 2015 Biophysical Society.
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