  We use a statistical mechanical model to study nonthermal denaturation of DNA
in the presence of protein-mediated loops. We find that looping proteins which
randomly link DNA bases located at a distance along the chain could cause a
first-order phase transition. We estimate the denaturation transition time near
the phase transition, which can be compared with experimental data. The model
describes the formation of multiple loops via dynamical (fluctuational) linking
between looping proteins, that is essential in many cellular biological
processes.
