A modified G-protein-coupled receptor (GPCR), having modified ligand affinity is provided by binding a G-protein-coupled receptor to a polypeptide consisting of an amino acid sequence of SEQ ID NO: 1. Furthermore, agonists for or antagonists against the modified GPCR are screened using a transformant in which the modified GPCR has been expressed. This makes it possible to provide a technique for analyzing the function of many putative GPCRs whose entities have not been clarified.
Methods of using an alpha-1-adrenergic receptor having altered ligand affinity