  Biopolymer looping is a dynamic process that occurs ubiquitously in cells for
gene regulation, protein folding, etc. In cellular environments, biopolymers
are often subject to tensions which are either static, or temporally
fluctuating far away from equilibrium. We study the dynamics of semiflexible
polymer looping in the presence of such tensions by using Brownian dynamics
simulation combined with an analytical theory. We show a minute tension
dramatically changes the looping time, especially for long chains. Considering
a dichotomically flipping noise as a simple example of the nonequilibrium
tension, we find the phenomenon of resonant activation, where the looping time
can be the minimum at an optimal flipping time. We discuss our results in
connection with recent experiments.
