IDENTIFICATION OF NEW MEDIATOR SUBUNITS IN THE RNA-POLYMERASE-II HOLOENZYME FROM SACCHAROMYCES-CEREVISIAE

Mediator was isolated from yeast on the basis of its requirement for t ranscriptional activation in a fully defined system. We have now ident ified three new members of mediator in the low molecular mass range by peptide sequence determination. These are the products of the NUT2, C SE2, and MED11 genes. The product of the NUT1 gene is evidently a comp onent of mediator as well. NUT1 and NUT2 were earlier identified as ne gative regulators of the HO promoter, whereas mutations in CSE2 affect chromosome segregation. MED11 is a previously uncharacterized gene. T he existence of these proteins in the mediator complex was verified by copurification and co-immunoprecipitation with RNA polymerase II holo enzyme.