A map of the hCGβ-LHβ gene cluster

The β-subunit of human chorionic gonadotropin (hCGβ) is reportedly encoded by as many as seven nonallelic genes or pseudogenes. Previous studies have identified a cluster of three hCGβ gene copies and the single-copy lutropin-β subunit (LHβ) gene, but overlap of this cluster with two additional pairs of hCGβ genes has not been demonstrated, despite the isolation of 18 genomic clones. To define the number and organization of non-allelic hCGβ gene copies, genomic Southern blot analyses were performed using hCGβ cDNA and gene-flanking unique-sequence probes. The data show the linear arrangement of six genes (or pseudogenes) and show that the hCGβ-IHβ gene cluster is present in a single 58-kilobase EcoRI fragment. Our map of the cluster indicates which of the cloned hCGβ genes reflect somatic genotypes rather than recombinant artifacts and will thus permit investigation of factors regulating expression during gestation.