Proper processing of a G protein gamma subunit depends on complex formation with a beta subunit.

G protein beta and gamma subunits function as a tightly associated complex. We show that complex formation with the beta subunit is a critical step for post-translational processing of a gamma subunit. When expressed alone in a cell line, the gamma 3 subunit type is isoprenylated but degraded; co-expression with the beta 1 subunit type stabilizes the gamma 3 protein. Furthermore, our experiments with partial cell fractionation indicate that the gamma 3 protein is localized differently in the cell depending on whether or not it is bound to the beta subunit. Binding of the gamma subunit to the beta subunit is thus one of the prerequisites for the appropriate intracellular localization of the beta gamma complex and potentially, for normal G-protein function.