Guanine nucleotide-binding proteins (G proteins) are involved as a modulator or transducer in various transmembrane signaling systems. The beta and gamma chains are required for the GTPase activity, for replacement of GDP by GTP, and for G protein-effector interaction. This subunit functions in visual transduction in the compound eye. G proteins are composed of 3 units, alpha, beta and gamma. Belongs to the G protein gamma family.