The basic mechanism of G protein-mediated transmembrane signaling was elucidated in the late 1970s and early 1980s. Subsequently, molecular clomng has identified a large array of closely related receptors (R), G protein subunits (G), and effecters (E). Currently, an important research goal is to understand the factors that, at each step of the cascade, link R to G to E, govern signal transfer, and signal integration following activation of a specific receptor (1 ). Receptors, in particular, appear to differ widely in their ability to interact with the different G protein oligomers and examples exist for stringent coupling of a receptor to a single species of a heterotrimer composed of a defined α-, β-, and γ-subunit, as well as promrscuous interaction with a wide variety of different G protein subunits (2 )