A Regulatory Element Within the Uteroferrin Gene 5′-Flanking Region Binds a Pregnancy-Associated Uterine Endometrial Protein

DNA–protein interactions within two putative regulatory regions distal from the transcription initiation site of the porcine uteroferrin (UF) gene were characterized. These regions, termed XB (−1,600 to −1,129 bp) and AB (−1,128 to −893 bp) exhibited transcriptional enhancer activities within the context of the heterologous SV40 promoter, that were specific to endometrial cells. DNase I and gel-shift assays demonstrated that both fragments contain a heptamer motif TGCTAGA that binds a nuclear protein present in crude and DEAE-fractionated nuclear extracts from porcine endometrium of pregnancy. This heptad sequence, designated as endometrial-associated sequence (EAS), is different from previously described nuclear protein-binding consensus sequences. Mutations in the heptamer motif abolished binding to the nuclear factor, as detected by gel-shift assays. The endometrial nuclear protein that interacts with the heptamer was characterized by Southwestern and UV cross-linking analysis. The protein has an approximate M _r of 80 kD, is basic (pI 7.7–8.6) and is present in pig endometrium throughout pregnancy. The functional relevance of this DNA-binding protein in the control of UF gene transcription in the endometrium is discussed.