Imposing Specificity by Regulated Localization
Many biologically important enzymes - RNA polymerases, RNA splicing
enzymes, ubiquinating enzymes, certain kinases and proteases - are
"regulated" by being brought to one or another of many potential
substrates by auxiliary docking proteins (e.g. transcriptional
activators). These regulatory interactions require interactions
between simple adhesive (but specific) surfaces. This kind of
regulation is highly 'evolvable' : new and expanded meanings to
signals are readily generated by simple changes in protein surfaces.