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 RARA/RXRA-mediated transcription. {ECO:0000269|PubMed:14657022, ECO:0000269|PubMed:14983011, ECO:0000269|PubMed:17641689}. This is the function of ENSG00000104973 (MED25, mediator complex subunit 25).