Uteroglobin is a small steroid-binding protein that is differentially regulated by steroid hormones in several tissues of the rabbit. In endometrium, the levels of uteroglobin mRNA increase after progesterone administration due to an enhanced rate of transcription of the uteroglobin gene. As a prerequisite for understanding the molecular mechanisms that modulate uteroglobin gene expression, we have isolated and characterized the uteroglobin gene. We first synthesized, cloned, and sequenced a uteroglobin cDNA that was used to screen a rabbit gene library and to show that the uteroglobin gene is not reiterated in the rabbit genome. We obtained three recombinant phages containing uteroglobin gene sequences and covering 35 kilobases of the rabbit genome. The uteroglobin gene is 3 kilobases long and is composed of three short exons separated by a long and a short intron. The complete coding sequence, the short intron, part of the large intron, and the flanking sequences have been subjected to sequence analysis. The salient features ofthe nucleotide sequence, including the absence of a canonical "T-A-T-A box," are discussed. A possible relationship is considered between the exon-intron structure of the gene and the known structure and function of uteroglobin.The induction of uteroglobin synthesis by steroid hormones in the rabbit offers a suitable system for studying the modulation ofgene expression in mammals (for a review, see ref. 1). In the endometrium progesterone is the main steroid inducer, whereas in the oviduct estrogens are effective inducers, and in the lung glucocorticoids cause a moderate induction of uteroglobin synthesis. We have shown in a cell-free transcription system that the accumulation of uteroglobin mRNA in endometrial cells after administration of ovarian hormones is mainly due to an increased rate of transcription of the uteroglobin gene (2).A more detailed understanding ofthe molecular mechanisms underlying the hormonal control ofuteroglobin gene expression depends on our knowledge of the structural organization of the gene and its putative regulatory sequences. An elucidation of the interaction between the hormone receptor and the regulatory sequences in chromatin may eventually provide answers to long-standing questions on the mechanism ofaction ofsteroid hormones.In this paper we report the synthesis, cloning, and sequence analysis of a uteroglobin cDNA and its use for the titration and isolation of the uteroglobin gene. The primary structure of the gene-coding sequences and the flanking regions is reported and discussed.MATERIALS AND METHODS Synthesis and Cloning of Double-Stranded Uteroglobin cDNA. The first cDNA strand was synthesized as previously described by using partially purified preuteroglobin mRNA as template (3). Actinomycin D was omitted and [3H]dCTP (specific activity 50 Ci/mmol; 1 Ci = 3.7 X 10'°becquerels) was used as the radioactive label. After alkaline hydrolysis the cDNA was isolated and a second strand was synthesized with reverse transcriptase and nonradioact...

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