Multicomponent transcription factor complexes: the exception or the rule?

Several functionally defined transcription factors have been described to lack the capacity for direct DNA binding. They are guided to their sites of function in promoter complexes by specific interactions with DNA- binding factors. This review explores both the phenomenon of binding dependence and the role of non-DNA-binding auxiliary factors in the context of several eukaryotic gene regulatory systems. The growing number of examples of multicomponent transcription factor complexes suggests that such additional levels of protein interaction and inferred control may be ubiquitous rather than exotic.