EXPRESSION OF 2 VARIANTS OF THE HUMAN MU-OPIOID RECEPTOR MESSENGER-RNA IN SK-N-SH CELLS AND HUMAN BRAIN

A partial mu opioid receptor gene was isolated from a human genomic li brary using a mouse delta opioid receptor cDNA as a probe. Using infor mation from this genomic clone and the published human mu receptor, MO R1, a cDNA was isolated from SK-N-SH mRNA that codes for a variant of the MOR1 mRNA, MOR1A. The presence of MOR1A is also shown in human bra in using RT-PCR. MOR1A differs from MOR1 in that the 3' terminal intro n has not been removed. An in-frame termination codon is found four am ino acids after the 5' consensus splice site, making MOR1A eight amino acids shorter than MOR1. Both receptors show similar ligand binding a nd coupling to cAMP in CHO-K1 cells. The C-terminal differences betwee n MOR1 and MOR1A could have effects on receptor coupling or receptor t ransport and localization.