Different classes of mammalian transcription factors-nuclear receptors, cyclic adenosine 3＇,5＇-monophosphate-regulated enhancer binding protein (CREB), and signal transducer and activator of transcription-1 (STAT-1)-functionally require distinct com ponents of the coactivator complex, including CREB-binding protein (CBP/p300), nuclear receptor coactivators (NCoAs), and p300/CBP-associated factor (p/CAF), based on their platform or assembly properties. Retinoic acid receptor, CREB, and STAT-1 also require different histone acetyltransferase (HAT) activities to activate transcription. Thus, transcription factor-specific differences in configuration and content of the coactivator complex dictate requirements for specific acetyltransferase activities, providing an explanation, at least in part, for the presence of multiple HAT components of the complex.