DRIP co-activator complex and assembly
The DRIP co-activator complex is a subset of 14 proteins from the set of at least 31 Mediator proteins that, in different combinations, form "Adapter" complexes. Adapter complexes bridge between the basal transcription factors (including Pol II) and tissue-specific transcription factors (TFs) bound to sites within upstream Proximal Promoter regions or distal Enhancer regions (reviewed in Maston, 2006 and Naar, 2001).
The DRIP complex was originally identified and named as a co-activator complex associated with the Vitamin D Receptor member of the nuclear receptor family of transcription factors (Rachez, 1998). It was later determined that all of the components of the DRIP complex were also in the TRAP complex, and the ARC complex.
The DRIP complex contains the following 14 proteins, which also are common to the ARC and TRAP complexes: MED1, MED4, MED6, MED7, MED10, MED12, MED13, MED14, MED16, MED17, MED23, MED24, CDK8, CycC.
All of the DRIP adapter complex components are present in the ARC adapter complex, but the ARC complex also has 4 additional components (Rachez, 1999). These ARC-specific components are now called: MED8, MED15, MED25, and MED 26 in the unified nomenclature scheme (Bourbon, 2004).
Similarly, all 14 of the DRIP adapter complex components are present in the TRAP adapter complex, but the TRAP complex also has 4 additional components (Bourbon, 2004), These TRAP-specific components are now called: MED20, MED27, MED30, and MED 31 in the unified nomenclature scheme.
In addition, these various transcription co-activator proteins identified in mammalian cells were found to be the orthologues or homologues of the Mediator complex identified in yeast, first identified by Kornberg and colleagues (Kelleher, 1990).