Med28 is a subunit of the large protein complex Mediator, a central coregulator of transcription in eukaryotes. In plants, Med28 mutants are affected in root development and senescence, phenotypes that are possibly associated to redox changes [].
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 [, ]. 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 []. Subunit Med28 of the Mediator may function as a scaffolding protein within Mediator by maintaining the stability of a submodule within the head module, and components of this submodule act together in a gene-regulatory programme to suppress smooth muscle cell differentiation. Thus, mammalian Mediator subunit Med28 functions as a repressor of smooth muscle-cell differentiation, which could have implications for disorders associated with abnormalities in smooth muscle cell growth and differentiation, including atherosclerosis, asthma, hypertension, and smooth muscle tumours [].
