The human adenosine A_2a receptor (A_2aR) belongs to the family of G-protein coupled receptors (GPCRs), characterized by seven transmembrane (TM) helices. TMs are involved in various cellular processes including dimerization-mediated recognition of ligand. TM5 has been suggested to self associate and may be involved in the dimerization of A_2aR. However the role of dimerization and the motifs involved in dimerization of TM 5 have not been revealed. To study the folding and assembly of A_2aR, the cDNA of the adenosine A_2aR from rat brain was isolated and sequenced (DQ098650). The computational analysis (gi|70727927|gb|AAZ07991.1|) showed that the protein of 42 amino acid residues aligned in TM 5 domain region of AA2AR_RAT (P30543). PROSITE search illustrated that the motif PMNYM was conserved in A_2aR and the motif PMSYM was present in A_2bR respectively. The minimal dimerization motif in the TM 5 domain of the rat A_2a receptor sequence DQ098650 has found to be the motif PXXXM/Y.