Identification of Optimized Target Sequences for the GLI3 Zinc Finger Protein

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Abstract
GLI3 represents an important control gene for development and differentiation of several body structures. Reduction in gene dosage already leads to a severe perturbation, especially of limb morphogenesis. The gene encodes a zinc linger protein that likely functions as a transcriptional modulator. Because the five zinc fingers should be capable of recognizing an extended stretch of genomic DNA, we sought to identify sequences bound by GLI3 that may facilitate the search for target genes acting downstream of GLI3. Starting from the nonamer DNA binding sequence of the highly related GLI protein, we employed an oligonucleotide selection protocol to determine an optimized binding sequence for the GLI3 protein. The resulting sequence bound by the GLI3 zinc fingers consists of 16 nucleotides and shows a high degree of similarity to sequences bound by the GLI and tra1 proteins. Comparison with protein-DNA interactions in the known crystal structure of the GLI-DNA complex suggests relevant interactions of additional amino acids of GLI3 with its target site. The newly identified GLI3 target sequence should prove very useful for both the structural analysis of the protein-DNA complex and the search for genes whose expression is subject to regulation by the GLI3 gene product.