A 5′-flanking sequence essential for progesterone regulation of an ovalbumin fusion gene

Ovalbumin gene transcripts are not detectable in unstimulated chick oviducts but comprise about half of oviduct cell transcripts after steroid hormone induction 1–3 . This seems to result mostly from an increased level of transcription 1–3 . When steroid hormones enter the cytoplasm of target cells they bind to specific receptors and the steroid–receptor complex accumulates in the nucleus 4,5 . Presumably this complex then binds in a sequenceor conformation-specific way near the regulated gene and enhances transcription. Several recent studies have shown that steroid hormone receptors bind preferentially to the 5′-flanking region of steroid-responsive genes in vitro 6–11 . Transcription of cloned genes for α 2u globulin 12 , growth hormone 13,14 , mouse mammary tumour virus 15–19 and lysozyme 20 can be induced in vivo by steroid hormones after transfer to cells containing steroid hormone receptors. In some of these studies, 5′-flanking regions were shown to be important for steroid regulation. We have now constructed a hybrid gene containing the ovalbumin gene promoter fused to the chicken adult β -globin gene and transferred it into primary cultures of chicken oviduct cells. We show that progesterone-mediated induction of transcription in untransformed oviduct cells depends on an ovalbumin gene flanking sequence between positions −95 and −222.