A PHYSICO-CHEMICAL INVESTIGATION OF THE SELF-ASSOCIATION OF THE DNA BINDING DOMAIN OF THE YEAST TRANSCRIPTIONAL ACTIVATOR GAL 4

It has previously been suggested that the DNA binding domain (residues 1 to 147) of the yeast transcriptional activator GAL4 exists in solution in dimeric form, with the region responsible for dimerisation somewhere between residues 74 and 147. In this study limited proteolysis and carboxy-terminal deletions of the DNA binding domain (residues 1 to 147) of the yeast transcriptional activator GAL4 followed by subsequent characterization by equilibrium sedimentation in the analytical ultracentrifuge have been used to define more precisely the regions required for DNA binding and protein self-association. Sedimentation equilibrium analyses confirmed that the ‘hydrophobic region’ of the protein (residues 54–97, which contains a larger proportion of α-helix), is essential for dimerisation, with an apparent dissociation constant KD,app, of ≈50 μM for the 1–94 residue peptide and ≈20 μM for the 1–147 residue peptide. Our studies do not rule out the possible formation of small amounts of additional higher order complexes.