DNA bending is a determinant of binding specificity for a Drosophila zinc finger protein

The suppressor of Hairy-wing [su(Hw)] locus encodes a zinc finger-containing protein that binds to specific sequences of the Drosophila gypsy element, mediating the mutagenic effects of this retrotransposon. We carried out a detailed analysis of the su(Hw)-gypsy interaction using various biochemical assays. DNase I footprinting delimits a 37-bp region in the coding strand of gypsy that is protected from digestion by the binding of the su(Hw) protein. Specific DNA contacts involved in the interaction were determined by methylation protection analysis and by missing nucleoside experiments using hydroxyl radical. Results from these experiments indicate that the su(Hw) protein binds to sequences homologous to the octamer motif, which is recognized by homeo box-containing proteins in mammalian organisms. Furthermore, two DNA bends present on both sides of the binding site in the absence of protein favor the strength of this interaction.