Transcriptional coactivator complexes

The last two decades have witnessed a tremendous expansion in our knowledge of the mechanisms employed by eukaryotic cells to control gene activity. A critical insight to transcriptional control mechanisms was provided by the discovery of coactivators, a diverse array of cellular factors that connec t sequence-specific DNA binding activators to the general transcriptional m achinery, or that help activators and the transcriptional apparatus to navi gate through the constraints of chromatin. A number of coactivators have be en isolated as large multifunctional complexes, and biochemical, genetic, m olecular, and cellular strategies have all contributed to uncovering many o f their components, activities, and modes of action. Coactivator functions can be broadly divided into two classes: (a) adaptors that direct activator recruitment of the transcriptional apparatus, (b) chromatin-remodeling or -modifying enzymes. Strikingly, several distinct coactivator complexes none theless share many subunits and appear to be assembled in a modular fashion . Such structural and functional modularity could provide the cell with bui lding blocks from which to construct a versatile array of coactivator compl exes according to its needs. The extent of functional interplay between the se different activities in gene-specific transcriptional regulation is only now becoming apparent, and will remain an active area of research for year s to come.