Isolation and characterization of an avian A1 adenosine receptor gene and a related cDNA clone

We have isolated the gene for a chick A1 adenosine receptor along with a cDNA that codes for the same adenosine receptor. The cDNA clone was isolated from both adipose tissue and heart cDNA libraries and encodes a 324-amino acid protein with 80% identity with mammalian A1 adenosine receptors. Transient expression of the cDNA in human embryonic kidney (HEK) 293 cells shows that it encodes a protein that binds [3H]CCPA (2-chloro-N6-[cyclopentyl-2,3,4,5-3H]cyclopentyladenosine, a specific agonist radioligand, with a KD of 5.6 +/- 2.4 nM. Cyclic AMP measurements in HEK 293 cells co-transfected with the chick cDNA and a cDNA for a luteinizing hormone/choriogonadotropin receptor shows that A1 adenosine receptor agonists antagonize the cyclic AMP-elevating effect of bovine luteinizing hormone. Two partial genomic clones were isolated. The first contains 5'-untranslated sequence including a putative promoter region which does not contain a TATA box, an intron and the first third of the coding sequence of the A1 adenosine receptor cDNA. The coding sequence of this partial genomic clone terminates at a second intron. The second partial genomic clone contains the rest of the coding sequence and the 3'-untranslated elements in a single exon. Thus the chick A1 adenosine receptor gene contains one intron in the 5'-untranslated region and a minimum of one intron in the coding sequence.