Dynamics of taut DNA chains

We discuss the dynamics of stretched DNR chains, subjected to a tension for ce f, in a "taut" regime where phi = fl(p0)/k(B)T > 1 (l(p0) being the unpe rturbed persistence length). We deal with two variables: the local transver se displacements u, and the longitudinal position of a monomer u(parallel t o). The variables u and u(parallel to) follow two distinct Rouse equations, with diffusion coefficients D-perpendicular to = f/eta (where eta is the s olvent viscosity) and D-parallel to = 4 phi(1/2)D(perpendicular to). We apply these ideas to a discussion of various transient regimes.