Binding studies with mutants of Zif268 - Contribution of individual side chains to binding affinity and specificity in the Zif268 zinc finger-DNA complex

The Zif268 zinc finger-DNA complex has served as a model system for underst anding how Cys,His, type zinc fingers recognize DNA. Structural studies of the Zif268-DNA complex revealed that residues at four positions in the cw h elix of each zinc finger play key roles in recognition, but there has been no information about the precise contributions of individual residues. Here we report the results of binding studies involving five mutants of Zif268 that have changes in the base contacting residues of finger one. These stud ies let us evaluate the contributions that Arg(18) (position -1 of the alph a helix), Asp(20) (position 2), Glu(21) (position 3), and Arg(24) (position 6) make to the overall energy of DNA binding. Our results confirm the impo rtant role played by these arginines. By comparing the affinities of the wi ld type and mutant peptides for various sites, we also prove that Asp(20) a nd Glu(21) play important roles in determining binding site specificity.