Component of the Mediator complex, a coactivator involved in the regulated transcription of nearly all RNA polymerase II-dependent genes. Mediator functions as a bridge to convey information from gene-specific regulatory proteins to the basal RNA polymerase II transcription machinery. Mediator is recruited to promoters by direct interactions with regulatory proteins and serves as a scaffold for the assembly of a functional preinitiation complex with RNA polymerase II and the general transcription factors. Required for cholesterol-dependent gene regulation. Positively regulates the Nodal signaling pathway (By similarity). Component of the Mediator complex, which is composed of MED1, MED4, MED6, MED7, MED8, MED9, MED10, MED11, MED12, MED13, MED13L, MED14, MED15, MED16, MED17, MED18, MED19, MED20, MED21, MED22, MED23, MED24, MED25, MED26, MED27, MED29, MED30, MED31, CCNC, CDK8 and CDC2L6/CDK11. The MED12, MED13, CCNC and CDK8 subunits form a distinct module termed the CDK8 module. Mediator containing the CDK8 module is less active than Mediator lacking this module in supporting transcriptional activation. Individual preparations of the Mediator complex lacking one or more distinct subunits have been variously termed ARC, CRSP, DRIP, PC2, SMCC and TRAP. Interacts with SMAD2, SMAD3, SREBF1 and SREBF2. Interacts with WWTR1 (By similarity). Interacts with TRIM11 (By similarity). At 9.5 dpc ubiquitously expressed at low levels with slightly elevated levels in the pharyngeal arches and in the forelimb buds. At 10.5 dpc expression was more pronounced in the first and second pharyngeal arches, the nasal processes and the limb buds. At 11.5 dpc expression is high in frontonasal region, maxillary and mandibular processes of the first and second pharyngeal arch and developing fore and hindlimbs. From 11.5 dpc-12.5 dpc expression is seen in the distal parts of the developing limbs and in the facial region. At 12.5 dpc transcripts were found in the developing hair follicles of the vibrissae. Ubiquitinated by TRIM11, leading to proteasomal degradation. Belongs to the Mediator complex subunit 15 family.