Dopamine $D_2R$ and $D_3R$ $(D_2R,;D_3R)$ show very high sequence homology and employ virtually identical signaling pathways even though $D_2R$ is $2{sim}5$ times more active. Among the structural motifs identified, a triplet sequence, Asp-Arg-Tyr (DRY motif), plays critical roles in the determination of receptor conformations for signaling and intracellular trafficking of G protein-coupled receptors by forming intramolecular interactions. Thus, it is possible that different signaling efficiencies of $D_2R$ and $D_3R$ might be caused by the receptor activation levels stabilized by their own DRY motifs. In this study, the Arg and Asp residues of $D_2R$ and $D_3R$ were mutated, and resulting changes in their signaling and intracellular trafficking properties were comparatively studied. Mutation of the Arg residues of $D_2R$ and $D_3R$ abolished their signaling but differently affected their intracellular localizations. The wildtype and $R132H-D_2R$ were expressed mainly on the plasma membrane. On the other hand, compared with the wildtype $D_3R$, a substantial amount of $R128H-D_3R$ was localized intracellularly. The expression of receptor proteins on the plasma membrane and their signaling efficiencies were more drastically affected by the mutation of the Asp residue of $D_3R$ than $D_2R$. Therefore, it was concluded that the different levels of conformational strain exerted by the DRY motif might partly determine the quantitative differences in the signaling efficiencies between $D_2R$ and $D_3R$.