Mediator is an essential, large, multisubunit, transcriptional co-activator highly conserved across eukaryotes. Mediator interacts with gene-specific transcription factors at enhancers as well as with the RNA polymerase II (RNAPII) transcription machinery bound at promoters. It also interacts with several other factors involved in various aspects of transcription, chromatin regulation, and mRNA processing. Hence, Mediator is at the nexus of RNAPII transcription, regulating its many steps and connecting transcription with co-transcriptional events. To achieve this flexible role, Mediator, which is divided into several functional modules, reorganizes its conformation and composition while making transient contacts with other components. Here, we review the mechanisms of action of Mediator and propose a unifying model for its function.

介体是必需的，大的，多亚基的转录共激活因子，在整个真核生物中高度保守。介体与增强子上的基因特异性转录因子以及与启动子结合的RNA聚合酶II（RNAPII）转录机制相互作用。它还与涉及转录，染色质调节和mRNA加工各个方面的其他几个因素相互作用。因此，介体处于RNAPII转录的纽带，调节其许多步骤并将转录与共转录事件联系起来。为了发挥这种灵活的作用，分为多个功能模块的介体在与其他组件进行短暂接触的同时重新组织了其构造和组成。在这里，我们回顾了介体的作用机理，并提出了其功能的统一模型。