Abstract
The Drosophila chorion factor 1/ultraspiracle transcription factor is a developmentally important member of the nuclear hormone receptor superfamily, and this factor most closely resembles the vertebrate retinoid X receptors. We describe here the expression of the CF1/USP protein in an E. coli T7 RNA polymerase-driven expression system. Using partially purified, bacterially produced CF1/USP, we have determined the equilibrium dissociation constant of this protein to its response element on the chorion s15 promoter. The equilibrium binding activity of CF1/USP to its chorion promoter is equivalent to the binding activities of other nuclear hormone receptors to their cognate elements.
