SPECIFICITY OF G-PROTEIN ALPHA-GAMMA SUBUNIT INTERACTIONS - N-TERMINAL 15 AMINO-ACIDS OF GAMMA-SUBUNIT SPECIFIES INTERACTION WITH ALPHA-SUBUNIT

The existence of multiple alpha, beta, and gamma subunits raises quest ions regarding the assembly of particular G proteins. Based on the res ults of a previous study (Rahmatullah, M., and Robishaw, J. D. (1994) J. Biol. Chem. 269, 3574-3580), we hypothesized that the assembly of G proteins may be determined by the interactions of the more structural ly diverse alpha and gamma subunits. This hypothesis was confirmed in the present study by showing striking differences in the abilities of the gamma(1) and gamma(2) subunits to interact with the the alpha(o) s ubunit. Chimeras of the gamma(1) and gamma(2) subunits were used to de lineate which region is responsible. Support for the importance of the N-terminal region of the gamma subunit comes from our observations th at 1) the gamma(2) subunit and the gamma(211) chimera bound strongly t o the alpha(o)-agarose matrix, but the gamma(1) subunit and the gamma( 112) chimera bound weakly, if at all; 2) an N-terminal peptide made to the gamma(2) subunit blocked the binding of the gamma(211) chimera to the alpha(o) agarose matrix; 3) both the gamma(211) chimera and the N -terminal peptide were able to partially protect the alpha(o) subunit against tryptic cleavage; and 4) the gamma(211) chimera, but not the g amma(112) chimera, supported ADP-ribosylation of the alpha(o) subunit.