Characterization of the Murine Orphan G-protein-coupled Receptor Gene Rai3 and Its Regulation by Retinoic Acid

A retinoic acid-inducible gene (RAI3) encoding an orphan G-protein-coupled receptor is regulated during embryonal carcinoma differentiation. To elucidate the mechanisms that mediate its regulation, we isolated and characterized the mouse gene (Rai3) and promoter region. Rai3 spans about 18 kb containing four exons separated by three introns and maps to mouse chromosome 6 near D6mit25. A functional analysis of the Rai3 gene promoter revealed that the proximal region harbors most of the elements necessary for its regulation, including GC boxes and Sp1-, AP1-, and AP2-binding sites. A functional retinoic acid response element direct repeat of two novel motifs separated by a 5-bp spacer (5'-TGTCCCtcggtTCACCC-3') was identified at -64 bp upstream of the transcription start site using the methods of promoter truncation, electrophoretic mobility shift assay, and mutation analysis. These findings provide strong evidence that Rai3 is regulated directly by retinoic acid via its receptors.