ABSTRACT Regions of the hamster a1-adrenergic receptor (aAR) EXPERIMENTAL PROCEDURES Plasmids. For the construction of chimeric 132/aiAR, residues 228-295 of the hamster a1AR (1) were substituted for residues 224-274 of the human fi2AR (6) by splicing the desired restriction fragments of DNA encoding the wild-type receptors with synthetic oligonucleotide adapters. For expression studies, the f32AR and chimeric P2/aAR were subcloned into the expression vector pBC12BI (18) as described (19). For construction of the ajAR mutants, singlestranded DNA was prepared from pTZ18R (Pharmacia) containing the cDNA of the a1AR and used for oligonucleotidedirected mutagenesis (Amersham). The identity of each mutant was confirmed by dideoxy sequencing of single-and double-stranded DNA with Sequenase (United States Biochemical). For expression studies, the expression vector pBCa1 (19) was digested with Xho I and Apa I and ligated to the Xho I-Apa I restriction fragments of each mutated ajAR species to obtain pBC12BI plasmids containing the DNA for each mutated receptor. Mammalian Cell Expression. COS-7 cells were grown in Dulbecco's modified Eagle's medium (DMEM) supplemented with gentamicin (100 ,ug/ml) and 10%o fetal bovine serum (GIBCO). COS-7 cells were transfected by the DEAEdextran metho
