The rabbit uteroglobin gene. Structure and interaction with the progesterone receptor.

The study of the regulation of uteroglobin gene in the rabbit endometrium constitutes a model for analyzing the mechanism of action of progesterone in mammals. The gene has been cloned into lambda phage and sequenced. Comparison of the sequence of the gene with the amino acid sequence of preuteroglobin and the three-dimensional structure of uteroglobin established by crystal x-ray diffraction showed that the 3 exons correspond to different functional domains of the protein and that at least one of the splice junctions does not map at the surface of the protein. S1 mapping allowed us to define the RNA polymerase initiation site. No difference was observed when analyzing premessengers from the endometrium, where the gene is controlled by progesterone and estradiol, and from lung where the gene is constitutively expressed and not controlled by these hormones. In addition, S1 mapping revealed the existence of several minor transcription initiation sites. In the 5' flanking region between positions -33 and -24 there is the sequence AATACAAAAA which may correspond to a Goldberg-Hogness box. Two other A- and T-rich sequences were found further upstream from the gene, one of these preceding by about 30 nucleotides a minor start of transcription. No obvious feature, possibly related to steroid regulation, was observed in the nucleotide sequence. A fragment of the gene containing the "promoter" region (from nucleotide +10 to nucleotide -394) was preferentially retained on nitrocellulose filters after incubation with purified rabbit uterine receptor. A competitive binding assay was used to compare the affinity for the receptor of various DNA fragments. Labeled "promoter" region DNA was incubated with receptor and various concentrations of nonlabeled competing DNA, and the nitrocellulose-bound radioactivity was measured. This method showed the existence of several high affinity binding sites in the 5' part of the gene and in adjacent regions. However, no high affinity binding sites were observed in the 3' part of the gene. Also, within the "promoter" region there were at least two high affinity binding sites for the receptor.