Retinal Rods and Cones Have Distinct G Protein β and γ Subunits

Guanine nucleotide-binding proteins (G proteins) involved in transmembrane signal-transduction processes are heterotrimers composed of α, β, and γ subunits. The α subunit shows great diversity and is thought to confer functional specificity to a particular G protein. By contrast, the β and γ subunits appear much less diverse; in particular, the β subunit is believed to have no role in G protein specificity. Using immunocytochemistry, we found distinct distribution patterns for different β and γ subunits in the retina. In particular, rod and cone photoreceptors, which both subserve phototransduction but differ in light-response properties, have different β and γ subunits in their outer segments. Thus, the G protein mediating phototransduction shows cell-specific forms of the β and γ subunits in addition to the α subunit. This surprising finding supports the hypothesis that these subunits may also contribute to functional specificity of a G protein.