In order to identify the domains of the G$_{alpha}$16 subunit G protein that are responsible for its activation by the Interleukin-8 receptor, a serious of chimeras between G$_{alpha}$16 and G$_{alpha}$11 were assessed for their abilities to be activated by these receptors. Co-expression of IL-8 receptor and chimeras in which the carboxyl-terminal regions of G$_{alpha}$11 were replaced from 30 up to 156 amino acid residues with the corresponding regions of G$_{alpha}$16 demonstrated that C-terminal 156 amino acid residues of the G$_{alpha}$16 were not sufficient to confer IL-8 receptor interaction specificity. Testing of a reciprocal serious of chimeras composed of G$_{alpha}$16 sequences at the amino terminus and G$_{alpha}$11 sequences at the carboxyl terminals revealed that sequences extending from the amino tar- minus to amino acid 209 of G$_{alpha}$16 were sufficient to 7ndow the chimera with 75-80% of interaction specificity for 7-8-induced activation. These results suggest th,.7t combined interactions of the C-terminal 30 amino acid residues and certain domains extending from the arts.ino terminus to amino acid 209 of Gal 6 protein may be involved in its couplings to IL-8 receptor.tain domains extending from the arts.ino terminus to amino acid 209 of Gal 6 protein may be involved in its couplings to IL-8 receptor.