A complex array of double-stranded and single-stranded DNA-binding proteins mediates induction of the ovalbumin gene by steroid hormones

The transcriptional induction of the chicken ovalbumin gene by steroid hormones is abolished by inhibitors of protein synthesis such as cycloheximide, suggesting that a labile protein mediates this process. A steroid-dependent regulatory element (SDRE) has been identified in the 5′-flanking region of the gene between -900 and -780 that is required for induction by steroids. Additional transfection experiments limit the 5′-border of the SDRE to the region between -892 and -864. To investigate whether any of the proteins binding to the SDRE are affected by estrogen or cycloheximide, protein binding was investigated using DNase I and exonuclease III footprinting and gel mobility shift assays. These experiments demonstrate that labile proteins bind to the sequences between -900 and -860 and between -810 and -820. Four oviduct nuclear proteins, including one of the labile proteins, binding to the SDRE prefer single-stranded DNA (ssDNA) in a sequence-specific manner. The binding activity of three of these ssDNA-binding proteins is increased in oviduct nuclear protein extracts from estrogen-treated chicks. These data suggest that induction of the ovalbumin gene is mediated by a complex collection of ssDNA- and double-stranded DNA-binding proteins whose activities are in turn regulated by their short half-lives or by estrogen.