In eukaryotes, transcription is highly regulated and involves many multiprotein complexes. One of these complexes, the Mediator of transcriptional regulation, plays a crucial role in the activation of transcription by RNA polymerase II (Pol II), as it integrates the signals of specific transcription factors and stimulates the recruitment of Pol II (Soutourina, 2018). However, the complexity of Mediator has precluded a detailed understanding of its mechanisms of action, essential for the study of the regulation of gene expression. In humans, mutations that affect Mediator subunits lead to a number of pathologies, including cancers, which underscore the importance of understanding the Mediator function for human health.