  The construction of a nonautonomous mixed mKdV/sine-Gordon model is proposed
by employing an infinite dimensional affine Lie algebraic structure within the
zero curvature representation. A systematic construction of soliton solutions
is provided by an adaptation of the dressing method which takes into account
arbitrary time dependent functions. A particular choice of those arbitrary
functions provides an interesting solution describing the transition of a pure
mKdV system into a pure sine-Gordon soliton.
