The activation of gene transcription is a multistep process that is triggered by factors that recognize transcriptional enhancer sites in DNA. These factors work with co-activators to direct transcriptional initiation by the RNA polymerase II apparatus. Mediator of RNA polymerase II transcription subunit 1 encoded by MED1 is a subunit of the CRSP (cofactor required for SP1 activation) complex, which, along with TFIID, is required for efficient activation by SP1. Mediator of RNA polymerase II transcription subunit 1 is also a component of other multisubunit complexes e.g. thyroid hormone receptor-(TR-) associated proteins which interact with TR and facilitate TR function on DNA templates in conjunction with initiation factors and cofactors. It also regulates p53-dependent apoptosis and it is essential for adipogenesis. Mediator of RNA polymerase II transcription subunit 1 is known to have the ability to self-oligomerize.