Evaluating chick Galpha-interacting protein selectivity

Regulators of G-protein signaling (RGS) proteins constitute a large family of GTPase-accelerating proteins (GAPs) for heterotrimeric G proteins. More than 30 RGS genes have been identified in mammals. One of these, the Galpha-interacting protein (GAIP), interacts preferentially with members of the G(i/o) subfamily of G-protein alpha subunits in mammalian cells. A unique isoform of GAIP, derived from embryonic chicken dorsal root ganglion neurons, has a short N terminus that is only 41% identical to known mammalian orthologs. Consistent with this unique primary structure, chick GAIP has higher target specificity than its mammalian counterparts. This article describes both in vitro and in vivo methods used to characterize chick GAIP selectivity.