Imposing specificity by localization: mechanism and evolvability.

Cells detect extracellular signals by allostery and then give those signals meaning by 'regulated localization'. We suggest that this formulation applies to many biological processes and is particularly well illustrated by the mechanisms of gene regulation. Analysis of these mechanisms reveals that regulated localization requires simple molecular interactions that are readily used combinatorially. This system of regulation is highly 'evolvable', and its use accounts, at least in part, for the nature of the complexities observed in biological systems.