The study describes the purification, molecular cloning, and expression of the mammalian sigma1-binding site. The sigma1-binding site was purified as a 30-kDa protein from guinea pig liver using specific probes, (+)[³H]pentazocine and (−)[³H]azidopamil. The purified protein retained high affinity for several sigma-ligands, including haloperidol, pentazocine, and dityl-guanidine. Partial amino acid sequencing revealed no homology to known proteins, but the protein showed structural similarity to fungal proteins involved in sterol synthesis. The corresponding cDNA was cloned using degenerate oligonucleotides and cDNA library screening. The cDNA encoded a 25.3-kDa protein with at least one putative transmembrane segment. Expression in yeast cells showed pharmacological characteristics of the sigma1-binding site in brain and liver. Northern blot analysis showed high expression of sigma1-binding site mRNA in sterol-producing tissues, consistent with its ability to interact with steroids like progesterone. The sigma-receptor concept was introduced by Martin et al., who differentiated the psychomimetic effects of norallylmetazocine (SKF10,047) from those of morphine and ketocyclazocine. Sigma-receptors are now defined by their ability to bind several chemically unrelated drugs with high affinity. Two subtypes of sigma-binding sites have been proposed based on differences in their drug-binding profiles. Endogenous sigma-ligands are not known, although progesterone has been suggested as one of them. Possible sigma-site-mediated drug effects include modulation of glutamate receptor function, neurotransmitter response, neuroprotection, behavior, and cognition. Most studies suggest that sigma-binding sites are plasmalemmal elements of the signal transduction cascade. Drugs reported to be selective sigma-ligands were evaluated as antipsychotics. Due to the lack of structural and functional information, the pharmacological significance of sigma-binding sites remains enigmatic. The sigma1-binding site was purified and cloned, and its cDNA was expressed in yeast cells. The cDNA was sufficient to form a high-affinity drug-binding domain with all characteristics of mammalian sigma1-binding sites. The sigma1-binding site was identified by photolabeling with (-)[³H]azidopamil and confirmed by immunoprecipitation with anti-PBP45 antibodies. The purified sigma1-binding site was found to have a molecular mass of 24 ± 2 kDa. The cDNA was cloned and expressed in yeast, and the resulting protein showed high-affinity binding for (+)[³H]pentazocine and other sigma-ligands. The sigma1-binding site was found to be structurally unrelated to known mammalian proteins but showed homology with fungal proteins involved in sterol synthesis. Northern blot analysis showed high expression ofThe study describes the purification, molecular cloning, and expression of the mammalian sigma1-binding site. The sigma1-binding site was purified as a 30-kDa protein from guinea pig liver using specific probes, (+)[³H]pentazocine and (−)[³H]azidopamil. The purified protein retained high affinity for several sigma-ligands, including haloperidol, pentazocine, and dityl-guanidine. Partial amino acid sequencing revealed no homology to known proteins, but the protein showed structural similarity to fungal proteins involved in sterol synthesis. The corresponding cDNA was cloned using degenerate oligonucleotides and cDNA library screening. The cDNA encoded a 25.3-kDa protein with at least one putative transmembrane segment. Expression in yeast cells showed pharmacological characteristics of the sigma1-binding site in brain and liver. Northern blot analysis showed high expression of sigma1-binding site mRNA in sterol-producing tissues, consistent with its ability to interact with steroids like progesterone. The sigma-receptor concept was introduced by Martin et al., who differentiated the psychomimetic effects of norallylmetazocine (SKF10,047) from those of morphine and ketocyclazocine. Sigma-receptors are now defined by their ability to bind several chemically unrelated drugs with high affinity. Two subtypes of sigma-binding sites have been proposed based on differences in their drug-binding profiles. Endogenous sigma-ligands are not known, although progesterone has been suggested as one of them. Possible sigma-site-mediated drug effects include modulation of glutamate receptor function, neurotransmitter response, neuroprotection, behavior, and cognition. Most studies suggest that sigma-binding sites are plasmalemmal elements of the signal transduction cascade. Drugs reported to be selective sigma-ligands were evaluated as antipsychotics. Due to the lack of structural and functional information, the pharmacological significance of sigma-binding sites remains enigmatic. The sigma1-binding site was purified and cloned, and its cDNA was expressed in yeast cells. The cDNA was sufficient to form a high-affinity drug-binding domain with all characteristics of mammalian sigma1-binding sites. The sigma1-binding site was identified by photolabeling with (-)[³H]azidopamil and confirmed by immunoprecipitation with anti-PBP45 antibodies. The purified sigma1-binding site was found to have a molecular mass of 24 ± 2 kDa. The cDNA was cloned and expressed in yeast, and the resulting protein showed high-affinity binding for (+)[³H]pentazocine and other sigma-ligands. The sigma1-binding site was found to be structurally unrelated to known mammalian proteins but showed homology with fungal proteins involved in sterol synthesis. Northern blot analysis showed high expression of