The monomer of the yeast transcriptional activator GCN4 recognizes its dimer binding DNA target sites without dimerization

Dimerization is widely believed to be a requirement for the yeast transcriptional activator GCN4 to recognize its specific DNA target sites. We used the basic region (226–252) of the yeast transcriptional activator GCN4, both as a monomeric peptide and a disulfide-linked dimer to investigate the interaction of GCN4 peptides with the DNA target sites AP-1 and CRE. CD and ITC experiments suggest that the monomeric peptide GCN4-M recognizes the AP-1 and CRE target sites, but it has a weaker affinity with the DNA relative to the disulfide-linked dimer peptide GCN4-D. These results indicate that the basic region of GCN4 alone is sufficient for sequence-specific DNA binding, and that dimerization can stabilize the protein-DNA complex.