Comment on mobility-shift computations featuring cage effects.

Theoretical mobility-shift patterns are computed by solution of conservation equations for electrophoresis coupled with chemical reaction. The chemical reaction term is often formulated in terms of dissociation of the protein-DNA complex in a gel cage. This formulation assumes that once the dissociated protein escapes the cage, it goes down a sink and is totally lost. This implies that the concentration of the escaped protein is too low to affect significantly the rates of protein-DNA association along its migration pathway.