Efficient interaction with a receptor requires a specific type of prenyl group on the G protein γ subunit

Post-translational prenylation of the carboxyl-terminal cysteine is a characteristic feature of the guanine nucleotide-binding protein (G protein) γ subunits. Recent findings show that the farnesylated COOH-terminal tail of the γ1 subunit is a specific determinant of rhodopsin-transducin coupling. We show here that when synthetic peptides specific to the COOH-terminal tail of γ1 are chemically modified with geranyl, farnesyl, or geranylgeranyl groups and tested for their ability to interact with light activated rhodopsin, the farnesylated peptide is significantly more effective. These results show that an appropriate isoprenoid on the G protein γ subunit serves not only a membrane anchoring function but in combination with the COOH-terminal domain specifies receptor-G protein coupling.