ARC coactivator complex MED16 MED15 MED23 MED8 MED26 Formation of ARC coactivator complex ARC co-activator complex and assembly The ARC co-activator complex is a subset of 18 proteins from the set of at least 31 Mediator proteins that, in different combinations, form "Adapter" complexes in human cells. 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 ARC complex was originally identified and named as a co-activator complex associated with transcription activator proteins (reviewed in Malik, 2005 and references therein). It was subsequently determined that many of the components of the ARC complex are also in the DRIP complex, and in the TRAP complex.. The ARC complex contains the following 14 proteins, which also are common to the DRIP and TRAP complexes: MED1, MED4, MED6, MED7, MED10, MED12, MED13, MED14, MED16, MED17, MED23, MED24, CDK8, CycC. The ARC complex also contains 4 additional, ARC-specific components, which are now called: MED8, MED15, MED25, and MED 26 in the unified nomenclature scheme (Bourbon, 2004). In addition, these various transcription co-activator proteins identified in mammalian cells were found to be the orthologues or homologues of the Mediator complex proteins in yeast, first identified by Kornberg and colleagues (Kelleher, 1990). The unified nomenclature system for these adapter / co-activator proteins now labels them Mediator 1 through Mediator 31 (Bourbon, 2004). The order of addition of the ARC proteins during complex assembly is not fully determined, and may vary in different cell contexts. Therefore, ARC complex assembly is represented as a single reaction event, in which all 19 components assemble simultaneously into the ARC co-activator complex. Pubmed10235266 Pubmed15175151 Pubmed15896744 Pubmed16719718 Pubmed2163759 Pubmed9637681 Pubmed9653119 Reactome Database ID Release 43212352 Reactome, http://www.reactome.org ReactomeREACT_12480 Reviewed: Freedman, LP, 2008-02-25 20:35:15