Transfection of CHO cells with the cDNA clones was performed with Lipofectamine according to the manufacturer's instructions, and cells were grown under the selection pressure of Geneticin (1 mg/ml). Mixed CHO cell clones expressing 3HA-A118/N40-hMOPR or 3HA-G118/D40-hMOPR were established as described previously [31].
