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 cycl oheximide, suggesting that a labile protein mediates this process. A s teroid-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 t he 5'-border of the SDRE to the region between -892 and -864. To inves tigate whether any of the proteins binding to the SDRE are affected by estrogen or cycloheximide, protein binding was investigated using DNa se I and exonuclease III footprinting and gel mobility shift assays. T hese experiments demonstrate that labile proteins bind to the sequence s between -900 and -860 and between -810 and -820. Four oviduct nuclea r 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. The se 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.