DIFFERENTIAL ABILITY TO FORM THE G-PROTEIN BETA-GAMMA COMPLEX AMONG MEMBERS OF THE BETA-SUBUNIT AND GAMMA-SUBUNIT FAMILIES

We have determined the relative abilities of several members of the G protein beta and gamma subunit families to associate with each other u sing the yeast two-hybrid system. We show first that the mammalian bet a 1 and gamma 3 fusion proteins form a complex in yeast and that forma tion of the complex activates the reporter gene for beta-galactosidase . Second, the magnitude of reporter activity stimulated by various com binations of beta and gamma subunit types varies widely. Third, the re porter activity evoked by a particular combination of beta and gamma s ubunit types is not correlated with the expression levels of these sub -unit types in the yeast cells. Finally, the reporter activity shows a direct relationship with the amount of hybrid py complex formed in th e cell as determined by immunoprecipitation, These results suggest tha t different beta and gamma subunit types interact with each other with widely varying abilities, and this in combination with the level of e xpression of a subunit type in a mammalian cell determines which G pro tein will be active in that cell. The strong preference of all gamma s ubunit types for the beta 1 subunit type explains the preponderence of this subunit type in most G proteins.