Organization, structure, and expression of the gene encoding the rat substance P receptor.

The gene for the rat substance P receptor has been cloned, its genomic structure determined, and the patterns of mRNA expression extensively analyzed. Unlike many genes encoding G protein-coupled receptors, the protein-coding region of this gene is divided into five exons consisting of 965, 195, 151, 197, and 2,010 base pairs. The substance P receptor gene extends more than 45 kilobases in length, and the splice sites for the exons occur at the borders of the sequences encoding putative membrane-spanning domains. The transcription initiation site has been defined by solution hybridization-nuclease protection and nucleotide sequence analyses, and lies downstream of a conventional TATA sequence. Substance P receptor mRNA levels in various tissues have been quantitated using solution hybridization-nuclease protection assays and were found to comprise from 0.00008 to 0.0016% of total RNA levels. Relatively high levels of substance P receptor mRNA are seen in the urinary bladder and the sublingual salivary gland, whereas moderate levels are observed for the submandibular salivary gland, striatum, hippocampus, midbrain, and olfactory bulb with lower levels in the remainder of the central nervous system and alimentary canal. These results are discussed in relation to the evolutionary role of multiple exons for a G protein-coupled receptor and with regard to the locations and mechanisms of substance P receptor gene expression.