Human dopamine D5 receptor pseudogenes

Molecular cloning studies have now identified five structurally homologous genes encoding the biosynthesis of the human dopamine receptors, DRD1, DRD2, DRD3, DRD4, and DRD5. Two of these dopamine receptors (DRD1 and DRD5) are encoded by intronless genes. To ascertain whether there are other intronless genes that share identity with the gene (DRD5) encoding the DRD5 receptor, we used a cloning method based on the polymerase chain reaction (PCR). Human genomic DNA was amplified by PCR with oligodeoxyribonucleotides (oligos) based on the DRD5 nucleotide (nt) sequence. Amplification of nt sequences between these oligos allowed the isolation of two independent intronless genes that share identity with DRD5. The full-length clones have also been isolated by screening human genomic libraries. The deduced amino acid sequences for these genes, PG-1 and PG-2, share 91% and 92% identity to DRD5, respectively. However, each of the genes contains differences in the coding regions that would render these genes incapable of encoding functional receptors. Thus, the human genome contains at least two DRD5 pseudogenes, consistent with in situ human chromosomal hybridization analysis which reveals the presence of two pseudogenes.