ACCELERATED COMMUNICATION A Major Species of Mouse -opioid Receptor mRNA and Its Promoter-Dependent Functional Polyadenylation Signal

The pharmacological effects of opioid drugs are mediated mainly by the -opioid receptor (MOR), which is encoded by an mRNA transcript named MOR1. Although several MOR mRNA splice variants have been reported, their biological relevance has been debated. In this study, we found that probes of regions essential for the production of functional MOR, as well as that of the 3-downstream region of the MOR gene coding region, detected by Northern blot analyses, a major species of mature transcript MOR1 from mouse brain of 11.5 kilobases (kb). Although exon 3 probe detected an additional 3.7-kb transcript, this transcript was not detected by other probes, ruling out its ability to produce functional MOR. The 3-untrans-lated region (UTR) of MOR1 is contiguously extended from the end of the coding region, and uses a single polyadenylatio