MED23 is a crucial subunit of the Mediator complex that serves as a transcriptional coactivator bridging gene-specific regulatory proteins to RNA polymerase II machinery 1. The protein functions beyond transcription initiation, coordinating transcription elongation, mRNA processing, and termination through direct interactions with 3' end processing factors like CPSF via MED23-FIP1 connections 2. MED23 directly binds hundreds of 3' mRNAs and regulates transcription termination, with deficiency leading to readthrough events and fusion transcripts 2. The protein mediates ELK1-dependent transcriptional activation in response to Ras-MAPK signaling, with structural studies revealing that phosphorylated ELK1 binds MED23 through a hydrophobic sequence containing phosphorylated S383, inducing allosteric changes 1. Disease relevance includes intellectual disability, where the R617Q mutation disrupts gene expression by altering chr6 conformation and enhancer activities, particularly affecting the MED23-DACH1-IEG axis involved in neural development and memory 3. In cancer, MED23 plays oncogenic roles through various mechanisms including alternative polyadenylation regulation 4 and hepatocellular carcinoma progression via the MED23-IGF2-NQO1 axis 5. Clinical significance extends to therapeutic targeting, with compounds disrupting ELF3-MED23 interactions showing promise in HER2-overexpressing cancers 6.