STRUCTURE AND EXPRESSION OF AN OVINE ENDOMETRIAL OXYTOCIN RECEPTOR CDNA

A sheep endometrial oxytocin receptor (OTR) cDNA (1.5 kb) was isolated from a lambda-ZAP library using a reverse transcription-PCR product p robe generated from oestrous endometrial mRNA. The sheep OTR cDNA shar ed an overall similarity of 82% with human OTR cDNA, 85% with pig OTR cDNA and 76% with rat OTR cDNA. The encoded receptor was a 398 amino a cid polypeptide 94% similar to human OTR, 94% similar to pig OTR and 9 3% similar to rat OTR. The sheep OTR contained two additional amino ac ids compared with human OTR which were located in the highly GC-rich t hird intracytoplasmic loop. This region is thought to be associated wi th G protein coupling and signal transduction. Expression of the cDNA in Cos-7 cells and measurement of oxytocin-induced phosphoinositide tu rnover confirmed that it coded for a functional product. The affinity of the expressed receptor was comparable with that observed for the in vivo receptor.