Dynamics of force-induced DNA slippage.

We study the base pairing dynamics of DNA with repetitive sequences where local strand slippage can create, annihilate, and move bulge loops. Using an explicit theoretical model, we find a rich dynamical behavior as a function of an applied shear force f: reptationlike dynamics at f=f(c) with a rupture time tau scaling as N3 with its length N, drift-diffusion dynamics for f(c)<f<f(*), and a dynamical transition to an unraveling mode of strand separation at f=f(*). We predict a viscoelastic behavior for periodic DNA with time and force scales that can be programmed into its sequence.