G-PROTEIN GAMMA-SUBUNITS WITH ALTERED PRENYLATION SEQUENCES ARE PROPERLY MODIFIED WHEN EXPRESSED IN SF9 CELLS

The gamma subunits of heterotrimeric G proteins undergo post-translati onal prenylation and carboxylmethylation after formation of the beta g amma dimer, modifications that are essential for alpha-beta gamma, bet a gamma-receptor, and beta gamma-effector interactions, We have determ ined the specific prenyl group present on the beta(1) gamma(1), beta(1 ) gamma(2), and beta(1) gamma(3) dimers purified from baculovirus-infe cted Sf9 cells by specific binding to G protein cu subunits immobilize d on agarose, These recombinant dimers undergo the same post-translati onal modifications determined for gamma(1) and gamma(2) isolated from mammalian tissues, Furthermore, infection of Sf9 cells with a recombin ant baculovirus encoding an alteration of the gamma(1), CaaX sequence (gamma(1)-S74L) resulted in geranylgeranylation of the resulting gamma (1) subunit, and alteration of the gamma(2) CaaX sequence to CAIS (gam ma(2)-L71S) resulted in farnesylation, Both of these altered gamma sub units were able to associate stably with beta(1), and the resulting be ta gamma dimer bound tightly to alpha-agarose and eluted specifically with aluminum fluoride, These results indicate that Sf9 insect cells p roperly process the CaaX motif in G protein gamma subunits and are a u seful model system to study the role of prenylation in the protein-pro tein interactions in which the beta gamma subunits participate.