Analysis by atomic force microscopy of Med8 binding to cis-acting regulatory elements of the SUC2 and HXK2 genes of Saccharomyces cerevisiae

Med8 protein is a regulator that specifically binds to upstream activating sequences (UASs) of SUC2 promoter, to downstream repressing sequences (DRSs ) of the HXK2 gene and to the carboxy-terminal domain of the RNA polymerase II. Atomic force microscopy has allowed for direct visualization of Med8 i nteractions with a 305 bp fragment of SUC2 promoter and with a 676 bp fragm ent of HXK2 gene, containing respectively the UASs and DRSs regulatory regi ons. This approach has provided complementary information about the positio n and the structure of the DNA-protein complexes. Med8 binding to DNA resul ts in total covering of one of the two existing 7 bp motives (consensus, (A /C)(A/G)GAAAT) in the studied DNA fragments. No preference for binding eith er of the two UASs of SUC2 promoter as well as for the two DRSs of HXK2 gen e has been found. We also discuss whether this protein works as dimer or as a monomer, (C) 1999 Federation of European Biochemical Societies.