The orphan receptor cDNA RDC7 encodes an A1 adenosine receptor.

@article{Libert1991TheOR,
  title={The orphan receptor cDNA RDC7 encodes an A1 adenosine receptor.},
  author={Frédérick Libert and S. N. Schiffmann and Anne Lefort and Marc Parmentier and C. G{\'e}rard and Jacques E. Dumont and J J Vanderhaeghen and Gilbert Vassart},
  journal={The EMBO Journal},
  year={1991},
  volume={10}
}
The extensive amino acid sequence conservation among G protein‐coupled receptors has been exploited to clone new members of this large family by homology screening or by PCR. Out of four such receptor cDNAs we cloned recently, RDC7 corresponds to a relatively abundant transcript in the brain cortex, the thyroid follicular cell and the testis. We have now identified RDC7 as an A1 adenosine receptor. The A1 agonist CPA [N6‐cyclopentyladenosine] decreased by 80% cAMP accumulation in forskolin… 
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Parmacological characterization of this receptor transiently expressed in mammalian cells demonstrates that, despite its high homology to A 1 adenosine receptors of other species, the guinea pig A 1Adenosine receptor displays a unique pharmacological profile: high affinity for the Al-selective antagonist CPX, yet very low affinity for some Al- selective agonists such as CCPA, CHA and R-PIA.
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Parmacological characterization of this receptor transiently expressed in mammalian cells demonstrates that, despite its high homology to A 1 adenosine receptors of other species, the guinea pig A 1Adenosine receptor displays a unique pharmacological profile: high affinity for the Al-selective antagonist CPX, yet very low affinity for some Al- selective agonists such as CCPA, CHA and R-PIA.
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Observations show that the human A1AR is a high affinity receptor that has ligand binding properties similar to the rat A1 AR, human A 1AR mRNA is heavily expressed in brain and testis, and the gene encoding thehuman A1ar is present on the long arm of chromosome 1.
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References

Molecular Cloning: A Laboratory Manual
TLDR
The content has been entirely recast to include nucleic-acid based methods selected as the most widely used and valuable in molecular and cellular biology laboratories.