Identification by sequence analysis of a second rat brain cDNA encoding the dopamine (D2) receptor

A rat brain cDNA library constructed in lambda ZAP II was screened with three oligonucleotide probes based on the reported coding region of the D2 receptor gene, RGB-2. A complete cDNA clone, D2(8)-1, showing positive signals with the three probes was subsequently identified by restriction analysis and dideoxy sequence analysis to be a variant of the RGB-2 gene. Comparison of the two genes revealed almost complete homology except that D2(8)-1 contains an 87 bp insert within the protein coding region and 265 additional nucleotides 5' upstream from the 5' end reported for RGB-2. It is suggested that at least two mRNA species encoding for D2 receptors exist in rat brain, possibly resulting from alternative splicing of RNA.