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 (By similarity). Positively regulates the Nodal signaling pathway. Component of the Mediator complex. Interacts with srebf1 and srebf2 (By similarity). Interacts with smad2, smad3 and smad4. Expressed maternally and throughout embryogenesis. Belongs to the Mediator complex subunit 15 family.