Little is known about the specific domains of G protein β and γ subunits which interact with each other and with the α subunit. We used site-specific anti-peptide antibodies directed against β and γ subunits to investigate domains on β and γ subunits involved in α subunit interaction. Antibodies included four against the transducin (Gt) β subunit (residues 1-10 = MS, 127-136 = KT, 256-265 = RA, and 330-340 = SW) and two against the γ subunit (residues 2-12 = PV and 58-68 = PE). All antisera, when affinity-purified on peptide columns, yielded antibodies capable of recognizing the denatured cognate subunit on immunoblots, but only RA, SW, PV, and PE recognized native βγt subunits. Affinity purification of MS and KT antisera on columns of immobilized native Gt yielded antibodies capable of recognizing native βγt subunits. The functional effects of each antibody preparation on αt, -βγt, interaction were assessed by assaying the ability of the preparations to immunoprecipitate βγt subunits in the presence of excess a subunits and by testing the inhibition of βγt, -dependent ADP-ribosylation of αt, -subunits catalyzed by pertussis toxin. On the basis of the results, we conclude that the domains on βγt, which may be directly involved in αt-βγt interaction include the extreme amino terminus, residues 127-136 and 256-265 of βt and the carboxyl terminus of γt. The carboxyl-terminal region of βt, and the amino terminus of γt, are less likely to be directly involved in αt, -βγt, interaction.
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