Structural organization of the rat luteinizing hormone (LH) receptor gene.

The luteinizing hormone (LH)/human chorionic gonadotropin (hCG) receptor gene was isolated from rat liver genomic libraries and spanned at least 75 kilobase pairs from nucleotide -2057 of the 5'-flanking region to the 3'-noncoding end. The structural configuration of the coding region of the LH receptor gene consists of 11 exons separated by 10 introns that are all located within the putative extracellular domain prior to the first transmembrane region. The 5'-noncoding region contains several potential TATA boxes and SP1 promoter binding sites, as well as six palindromic elements, potential intron/exon splice junctions, and two extended open reading frames in frame with the initiation codon. Primer extension studies indicate the presence of multiple transcriptional initiation sites. Truncated forms of the LH/hCG receptor conform to alternative splicing patterns that are consistent either with the deletion of complete exons or alternate acceptor sites within exons. All splice site junctions correspond to known donor and acceptor consensus sequences. Exons 2-8 approximate the regions of the 14 consecutive 20 amino acid repeated motifs present in the LH, thyrotropin-stimulating hormone, and follicle-stimulating hormone receptor cDNAs, with the exception of a six to eight amino acid shift in each motif. Exons 1, 9, 10, and 11, do not conform to this repetitive intronic motif. These exons, however, contain important structural elements including the conserved cysteines (exons 1, 9, 11), the soybean lectin motif (exon 9), the seven-transmembrane domain with cytoplasmic G protein coupling elements (exon 11), and three putative N-linked glycosylation sites (exon 10), consistent with preservation of significant functional domains within single exons. Exon 10 and the beginning of exon 11 along with the lectin motif are unique to the LH receptor and may be involved in specific association with the hormonal ligand. The homologous regions with other members of the glycoprotein receptor family encoded by exons 2-8, and the common amino acid motif that contains 3 conserved cysteines immediately prior to the first transmembrane region, may be involved in common hormonal interactions and in coupling functions, respectively.