Receptor-Effector Coupling by G Proteins: Purification of Human Erythrocyte G_i-2 and G_i-3 and Analysis of Effector Regulation Using Recombinant α Subunits Synthesized in Escherichia coli

Excerpt

Molecular cloning has revealed the existence of many more G proteins than anticipated from purification studies, especially in the field of G_s, where what originally were thought to be two forms of α_s (Mattera et al. 1986; Robishaw et al. 1986) turned out to be four splice variants (Bray et al. 1986; Kozasa et al. 1988), and G_i, of which there are now known to exist three independent genes, as deduced from cDNA cloning (Jones and Reed 1987; Suki et al. 1987) and gene sequencing (Itoh et al. 1988). The abundance at which different α_s and α_i molecules are expressed varies from tissue to tissue, raising the question as to whether functional differences are associated with the structural differences, or whether the G_s proteins and, respectively, the G_i proteins should be thought of merely as isoforms. Although the final word on this question is not yet in, we have developed...