It is shown how the complex sine-Gordon equation arises as a symmetry flow
of the AKNS hierarchy. The AKNS hierarchy is extended by the 'negative' sym
metry flows forming the Borel loop algebra. The complex sine-Gordon and the
vector nonlinear Schrodinger equations appear as lowest-negative and secon
d-positive flows within the extended hierarchy. This is fully analogous to
the well known connection between the sine-Gordon and mKdV equations within
the extended mKdV hierarchy. A general formalism for a Toda-like symmetry
occupying the 'negative' sector of the sl(N) constrained KP hierarchy and g
iving rise to the negative Borel sl(N) loop algebra is indicated.