The MED26 gene encodes a subunit of the CRSP (cofactor required for SP1 activation) Mediator complex, a regulatory complex involved in transcriptional activation and elongation. This complex, along with TFIID, is required for the efficient activation of transcription by the enhancer-binding factor SP1. By working within this complex, it is believed that the MED26 protein plays a role in the phosphorylation of the RNA polymerase II terminal domain, as well as in the recruitment of RNA polymerase II and the Super Elongation Complex (SEC) components AFF4 and CDK9 to the promoter regions of target genes. It is suggested that MED26 functions as a molecular switch, initially interacting with TFIID during transcriptional activation and then exchanging TFIID for polymerase II elongation factors to promote elongation. Through its actions MED26 is found to activate the expression of the MYC, HSP70 and SNAI2 genes.