Med8, a subunit of the mediator CTD complex of RNA polymerase II, directlybinds to regulatory elements of SUC2 and HXK2 genes

In a search to identify new factors required for expression of SUC2 gene in Saccharomyces cerevisiae, we have partially purified a 27 kDa protein (p27 ) that bound both the DRSs of the HXK2 gene and the UASs of SUC2 gene. The amino terminal sequence of p27 identified the MED8 gene (open reading frame YBR193C), located in chromosome II of S, cerevisiae, as the gene coding fo r the protein. Disruption of this gene has demonstrated that is an essentia l gene for yeast growth. To determine whether the p27 protein represents th e MedB product, we expressed MED8 gene in E. coli and demonstrated that the heterologous synthesized protein specifically binds to both UAS(SUC2) and DRS2(HXK2). This observation suggests that Med8 may be important for the co upling of the glucose repression pathway of SUC2 gene to the HXK2 gene expr ession. Med8 has been described as a mediator protein interacting with the CTD of the RNA polymerase II, Thus, the role of Med8 could be to act as cou pling factor by linking activating and repressing transcription complexes t o the RNA polymerase II holoenzyme transcriptional machinery, (C) 1999 Acad emic Press.