Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems. This specific G-alpha subunit plays an important role in olfaction and in cilia morphogenesis. Involved in chemotactic responses to attractants diacetyl, pyrazine, 2,4,5-trimethylthiazole, benzaldehyde, isoamyl alcohol, butanone and 2,3-pentanedione. Displays a redundant function with gpa-3 in chemotactic responses. Involved in avoidance responses to copper, sodium dodecyl sulfate and linoleic acid. Involved in osmotic avoidance and mechanosensory responses. Involved in specifying fan-like morphology of cilia of head sensory neurons AWC (By similarity). G proteins are composed of 3 units; alpha, beta and gamma. The alpha chain contains the guanine nucleotide binding site (By similarity). In amphid neurons also weakly expressed in cell body. In phasmid neurons found only in cilia. Belongs to the G-alpha family.