ELECTROSTATIC EFFECTS IN DNA BENDING BY GCN4 MUTANTS

DNA architecture has been shown ro be important for cellular processes such as activation of transcription, recombination, and replication. Many proteins reconfigure the shape of duplex DNA upon binding, Previo us experiments have shown that some members of the eukaryotic bZIP fam ily of DNA binding proteins appear to bend DNA, while others do not, W e are exploring the role of electrostatic effects in DNA bending by bZ IP proteins. The yeast bZIP transcription factor GCN4 does not induce DNA bending in vitro. Previously we substituted basic residues for thr ee neutral amino acids in GCN4 to produce a GCN4 derivative that bends DNA by similar to 15 degrees, This result is consistent with a model of induced DNA bending wherein excess positive charge in proximity to one face of the double helix neutralizes local phosphate diester anion s resulting in a laterally-asymmetric charge distribution along the DN A. Such an unbalanced charge distribution can result in collapse of th e DNA toward the neutralized surface, We now present a more comprehens ive analysis of electrostatic effects in DNA bending by GCN4 derivativ es. It is shown that the direction and extent of DNA bending by these derivatives are a linear function of the charges of the amino acids ad jacent to the basic domain of the protein. This relation holds over th e charge range +6 (16 degrees bend toward the minor groove) to -6 (25 degrees bend toward the major groove).