  The interaction between large internal motion of DNA surrounded by bio-fluid
is investigated. The phenomenon is modelled using the relativistic
Navier-Stokes lagrangian describing the bio-fluid coupled to the standard
Klein-Gordon lagrangian describing the DNA. It is shown that the equation of
motion at non-relativistic limit, v << c, reproduces the well-known Sine-Gordon
equation. The effect of the interaction in a single soliton solution is also
given and discussed.
