ORIGIN AND DIVERGENCE OF TANDEM REPEATS OF PRIMATE D4 DOPAMINE-RECEPTOR GENES

Human D4 dopamine receptor (D4DR) is polymorphic in terms of the repea t numbers of the 48-base pairs (bp) sequence located in the third cyto plasmic loop of the receptor. The repeated sequence and its polymorphi sm in D4DR genes have also been identified in higher non-human primate s, suggesting that the structure of D4DR has been maintained during pr imate evolution. To clarify the origin and divergence of the polymorph ism in the D4DR gene, we determined the nucleotide sequence of this re gion of the D4DR gene in several species of prosimians and the tree sh rew, a species which is closely related to primates. Prosimians except the tarsier had one or two unit(s) of the 48-bp sequence, and conserv ed sequences were recognized in most of the units of the prosimians. T he tree shrew had only one unit of the 48-bp sequence, and its sequenc e was 71-75% identical to those of the units of galago, loris, and lem ur. These findings suggest that the ancestral primate presumably had o ne 48-bp unit, and duplication of the unit occurred at the stage of pr osimians. Tarsiers appeared to be distinct from other prosimians and s imians because of the high repeat numbers of units and their sequences .