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TFIIS helical bundle-like domain Mediator is a large complex of up to 33 proteins that is conserved from plants to fungi to humans - the number and representation of individual subunits varying with species {1-2]. It is arranged into four different sections, a core, a head, a tail and a kinase-activity part, and the number of subunits within each of these is what varies with species. Overall, Mediator regulates the transcriptional activity of RNA polymerase II but it would appear that each of the four different sections has a slightly different function. Mediator exists in two major forms in human cells: a smaller form that interacts strongly with pol II and activates transcription, and a large form that does not interact strongly with pol II and does not directly activate transcription. Notably, the 'small' and 'large' Mediator complexes differ in their subunit composition: the Med26 subunit preferentially associates with the small, active complex, whereas cdk8, cyclin C, Med12 and Med13 associate with the large Mediator complex. This family includesthe C terminal region of a number of eukaryotic hypothetical proteins which are homologous to the Saccharomyces cerevisiae protein IWS1. IWS1 is known to be an Pol II transcription elongation factor and interacts with Spt6 and Spt5. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",