The Plant Mediator Complex in the Initiation of Transcription by RNA Polymerase II

Abstract

Thirty years have passed since the discovery of the Mediator complex inyeast.We are witnessing breakthroughs and advances that have led to high-resolution structural models of yeast and mammalian Mediators in thepreinitiation complex, showing how it is assembled and how it positionsthe RNA polymerase II and its C-terminal domain (CTD) to facilitate theCTD phosphorylation that initiates transcription. This information may bealso used to guide future plant research on the mechanisms of Mediatortranscriptional control. Here, we review what we know about the subunitcomposition and structure of plant Mediators, the roles of the individualsubunits and the genetic analyses that pioneered Mediator research, andhow transcription factors recruit Mediators to regulatory regions adjoiningpromoters. What emerges from the research is a Mediator that regulatestranscription activity and recruits hormonal signaling modules and histone-modifying activities to set up an off or on transcriptional state that recruitsgeneral transcription factors for preinitiation complex assembly.