Influence of gamma subunit prenylation on association of guanine nucleotide-binding regulatory proteins with membranes.

Two approaches were taken to address the possible role of gamma-subunit prenylation in dictating the cellular distribution of guanine nucleotide-binding regulatory proteins. Prenylation of gamma subunits was prevented by site-directed mutagenesis or by inhibiting the synthesis of mevalonate, the precursor of cellular isoprenoids. When beta or gamma subunits were transiently expressed in COS-M6 simian kidney cells (COS) cells, the proteins were found in the membrane fraction by immunoblotting. Immunofluorescence experiments indicated that the proteins were distributed to intracellular structures in addition to plasma membranes. Replacement of Cys68 of gamma with Ser prevented prenylation of the mutant protein and association of the protein with the membrane fraction of COS cells. Immunoblotting results demonstrated that some of the beta subunits were found in the cytoplasm when coexpressed with the nonprenylated mutant gamma subunit. When Neuro 2A cells were treated with compactin to inhibit protein prenylation, a fraction of endogenous beta and gamma was distributed in the cytoplasm. It is concluded that prenylation facilitates association of gamma subunits with membranes, that the cellular location of gamma influences the distribution of beta, and that prenylation is not an absolute requirement for interaction of beta and gamma.