Two gene duplication events in the human and primate dopamine D5 receptor gene family

The human dopamine D5 receptor (DRD5) gene family consists of the DRD5-encoding gene (DRD5) and the pseudogenes psi DRD5-1 and psi DRD5-2. Analysis of the 5' UTR of DRD5 and homologous regions in the pseudogenes revealed that the nucleotide identity (approx. 95%) extended for 1.9 kb and terminated at a monomeric Alu sequence in each of the pseudogenes. The presence of Alu sequences in the pseudogenes, at this point of divergence with DRD5, suggests that Alu sequences were involved in the evolution of the DRD5 family. This report is the first to describe a possible mechanism involved in the duplication of genes in the G-protein-coupled receptor (GPCR) family. The pseudogenes continue to share identity (approx. 98%) beyond this 5' UTR point of divergence with DRD5 for at least another 6 kb. Analysis of the 3' UTR of DRD5 and homologous regions in the pseudogenes revealed that the identity (approx. 95%) extends at least 14 kb, and the identity between the pseudogenes (approx. 98%) extends for at least 18 kb. Thus, the duplication unit that produced the first pseudogene was at least 16 kb, whereas the second pseudogene was at least 28 kb. We have also located two DRD5 pseudogenes in gorilla demonstrating that these closely related pseudogenes were present in a common ancestor of human and gorilla.