A. Suma, E. Orlandini and C. Micheletti
Knotting dynamics of DNA chains of different length confined in nanochannels
J. Phys. Condensed Matter, 2015, 27 , art no. 354102
Link to online article
Langevin dynamics simulations are used to characterize the typical mechanisms governing the spontaneous tying, untying and the dynamical evolution of knots in coarse-grained models of DNA chains confined in
nanochannels. In particular we focus on how these mechanisms depend on the chain contour length, $L_c$,
at a fixed channel width $D=56$nm corresponding to the onset of the Odijk scaling regime where
chain backfoldings and hence knots are disfavoured but not suppressed altogether.
We find that the lifetime of knots grows significantly with $L_c$, while that of unknots varies to a lesser extent.
The underlying kinetic mechanisms are clarified by analysing the evolution of the knot position along the chain. At the considered confinement, in fact, knots are typically tied by local backfoldings of the chain termini where they are eventually untied after a stochastic motion along the chain. Consequently, the lifetime of unknots is mostly controlled by backfoldings events at the chain ends, which is largely independent of $L_c$. The lifetime of knots, instead, increases significantly with $L_c$ because knots can, on average, travel farther along the chain before being untied.
The observed interplay of knots and unknots lifetimes underpins the growth of the equilibrium knotting probability of longer and longer chains at fixed channel confinement.