MOLECULAR-CLONING AND CHARACTERIZATION OF THE MOUSE DOPAMINE D-3 RECEPTOR GENE - AN ADDITIONAL INTRON AND AN MESSENGER-RNA VARIANT

The intron-exon organization for the murine dopamine D-3 receptor gene was determined. A novel intron of approximately 1 kb was identified i n both rat and mouse D-3 receptor genes. This intron (termed intron 4) is situated between coding nucleotides 723 and 724, resulting in a sp lit of former exon 4 (containing nucleotides 527-801) into two separat e exons (exon 4 and exon 5). Thus, the coding regions of the D-2 and D -3 receptor genes contain an identical number of exons (seven exons) a nd share a very similar gene structure. Reverse transcription-PCR expe riments revealed a short form of mouse D-3 mRNA (D-3Short) that lacks the first 63 nucleotides from exon 6, and results from a splicing even t occurring within this exon. However, this mRNA variant was not found in either rat or human brain. No dopamine D-3 receptor mRNA variants were found deriving from the alternative splicing of exon 5, although its counterpart, exon 6 in the D-2 receptor gene, is spliced out to pr oduce the D-2Short mRNA. These data suggest that, although the intron- exon organizations of the D-2 and D-3 receptor genes are similar, the encoded transcripts may be processed differently.