G protein diversity is increased by associations with a variety of γ subunits

Guanine nucleotide-binding regulatory proteins (G proteins) are heterotrimeric proteins that transduce extracellular signals into intracellular changes. Functionally different G proteins have been identified by their different α subunits. The β and γ subunits have been assumed to constitute a common pool shared among various G protein heterotrimers. Two γ subunits (γ₃ and γ₄) have been identified through molecular cloning; these are in addition to two subunits (γ₁ and γ₂) that were previously characterized. G proteins purified from a variety of mammalian tissues were examined with antisera specific to three of the γ subunits. The antisera react with different γ subunits associated with some of the purified G proteins but not all. This demonstrates that different G protein heterotrimers from different tissues carry structurally distinct members of the γ-subunit family. Diversity in the structure of the γ as well as the α and β subunits and preferential associations between members of subunit families increase structural and possibly functional diversity of G proteins.