Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems. The G(q) alpha subunit is involved in the light-dependent activation of phospholipase C. G proteins are composed of 3 units; alpha, beta and gamma. The alpha chain contains the guanine nucleotide binding site. A high concentration was found in the retinal light-sensitive outer segment. Belongs to the G-alpha family. G(q) subfamily.