DNA BENDING BY GCN4 MUTANTS BEARING CATIONIC RESIDUES

Transcription activation is thought to require DNA bending to promote the interaction of upstream activators and the basal transcription mac hinery. Previous experiments have shown that some members of the bZIP family of DNA binding proteins bend DNA, while others do not. We are e xploring the possibility that electrostatic effects play a role in the se differences, The yeast bZIP transcription factor GCN4 does not indu ce DNA bending in vitro. Substitution of basic residues for three neut ral amino acids of GCN4 confers the ability to bend DNA. This result i s consistent with a model of induced DNA bending wherein excess positi ve charge in proximity to one face of tile double helix neutralizes lo cal phosphate diester anions resulting in a laterally asymmetric charg e distribution along the DNA, Previous data suggest that such an unbal anced charge distribution results in collapse of the DNA toward the ne utralized surface, interpretations of the present data are discussed, Our result supports the hypothesis that electrostatic interactions can play a key role in DNA bending by bZIP proteins.