Characterization of the DNA binding activity of the ZFY zinc finger domain

The ZFY protein is a member of one of the most interesting classes of polydactyl zinc finger proteins. It has a domain of 13 tandem zinc fingers that is organized with an internal repeat of odd-even finger pairs. It has been proposed that each finger pair interacts with six base pairs within a turn of the double helix, the downstream linker crossing the minor groove to place the next finger pair on the following turn of the DNA. Yet putative binding sites for the full-length ZFY protein appear to consist of a six-base AGGCCY consensus sequence that is present in one or two copies. In this study the equilibrium binding of two ZFY-derived zinc finger peptides to 4R DNA with tandem copies of the consensus sequence was investigated. The ZFY5 peptide contains fingers 5-13, including four odd-even finger pairs, and the ZFY11 peptide contains fingers 11-13 and has one odd-even finger pair. Both peptides bound to 4R DNA with equal affinities, forming a bimolecular complex that is mediated by the downstream AGGCCY motif. The additional odd-even finger pairs in ZFY5 made no measurable difference in the mechanism of DNA binding compared to ZFY11. The effects on the DNA-protein interaction of mutations in the 4R DNA and in the key alpha-helical residues of fingers 11-13 indicate that the binding of ZFY to DNA is mediated by the interaction of the GGCC core base pairs with fingers 12 and 13. These results demonstrate that the even-odd repeats in the ZFY zinc finger domain do not make significant contributions to DNA binding.