Chimeric G(alpha) proteins, obtained by exchanging their C-terminal portion for that of a G(alpha) protein from an unrelated class, drive the receptor selectivity to that corresponding to the introduced G(alpha) protein domain. The alpha(2)A-adrenoceptor (alpha(2)AAR), which yielded an efficacious and weak [(3)5S]GTPgammaS binding response by respectively G(alphao) and G(alphai3) protein, was investigated in CHO-K1 cells co-expressing chimeric G(alpha) proteins for which the six last C-terminal amino acids between G(alphao) and G(alphai3) proteins, and reciprocally, were permuted. Activation of the chimeric G(alphao/i3) protein was highly efficient whereas the G(alphai3/o) protein yielded a weak stimulation. These [S-35]GTPgammaS binding responses were not different from their parental wild-type G(alphao) and G(alphai3) proteins. Similar results were obtained with an alpha(2)AAR carrying a facilitating Thr(373)Lys mutation in a putative G protein interaction domain. These data indicate that the six terminal G(alphao) protein amino acids do not constitute a major alpha(2)AAR interaction domain for G(alpha) protein activation.