In mechanical models of DNA, twist-bend coupling is a cross interaction term originating from the asymmetry between major and minor grooves. We show that such coupling induces minimal energy shapes of overtwisted DNA minicircles resembling rounded polygons, with a periodic alternance of parts with high and low curvature . The periodicity is close to that of the double helix and depends on the degree of overtwisting. From a simple elastic energy minimization ansatz we derive an analytical expression of the minicircle shape which matches very well the results obtained from simulations of various coarse-grained models of DNA. Finally, the calculation of the twist and bending energy of minicircles shows how these are governed by renormalized stiffness constants, not the bare ones. This has important consequences for the analysis of experiments involving circular DNA meant to determine DNA elastic constants.
By combining analytical results and simulations of various coarse-grained models we investigate the minimal energy shape of DNA minicircles which are torsionally constrained by an imposed over or undertwist. We show that twist-bend coupling , a cross interaction term discussed in the recent DNA literature, induces minimal energy shapes with a periodic alternance of parts with high and low curvature resembling rounded polygons. We briefly discuss the possible experimental relevance of these findings. We finally show that the twist and bending energies of minicircles are governed by renormalized stiffness constants, not the bare ones. This has important consequences for the analysis of experiments involving circular DNA meant to determine DNA elastic constants.
R
In mechanical models of DNA,
By combining analytical results and simulations of various coarse-grained models we investigate the minimal energy shape of DNA minicircles which are torsionally constrained by an imposed over or undertwist. We show that
R
is
,
R
originating from the asymmetry between major and minor grooves. We show that such coupling
discussed in the recent DNA literature,
D
of overtwisted DNA minicircles resembling rounded polygons,
R
. The periodicity is close to that of the double helix and depends on the degree of overtwisting. From a simple elastic energy minimization ansatz we derive an analytical expression of the minicircle shape which matches very well the results obtained from simulations of various coarse-grained models of DNA. Finally, the calculation of the
resembling rounded polygons. We briefly discuss the possible experimental relevance of these findings. We finally show that the
R
energy of minicircles shows how these
energies of minicircles