MED23: a new Mediator of H2B monoubiquitylation.

The Mediator multiprotein complex physically links transcription factors to RNA polymerase II and the basal transcription machinery. While the Mediator complex has been shown to be required for transcriptional initiation and elongation, the understanding of its interplay with histone modifying enzymes and post‐translational modifications remains elusive. In this issue of The EMBO Journal, Yao et al (2015) report that the MED23 subunit of the Mediator complex physically associates with the heterodimeric RNF20/40 E3‐ligase complex to facilitate the monoubiquitylation of histone H2B on gene bodies of actively transcribed genes.