Guanine nucleotide-binding proteins (G proteins) function as transducers downstream of G protein-coupled receptors (GPCRs) in numerous signaling cascades. The alpha chain contains the guanine nucleotide binding site and alternates between an active, GTP-bound state and an inactive, GDP-bound state. Signaling by an activated GPCR promotes GDP release and GTP binding. The alpha subunit has a low GTPase activity that converts bound GTP to GDP, thereby terminating the signal. Both GDP release and GTP hydrolysis are modulated by numerous regulatory proteins (By similarity). Signaling is mediated via effector proteins, such as adenylate cyclase. Inhibits adenylate cyclase activity, leading to decreased intracellular cAMP levels (By similarity). Required for cortical dynein-dynactin complex recruitment during metaphase (By similarity). Heterotrimeric G proteins are composed of 3 units; alpha, beta and gamma. The alpha chain contains the guanine nucleotide binding site. Part of a spindle orientation complex. Identified in complex with the beta subunit GNB1 and the gamma subunit GNG1. Identified in complex with the beta subunit GNB1 and the gamma subunit GNG2. GTP binding causes dissociation of the heterotrimer, liberating the individual subunits so that they can interact with downstream effector proteins (By similarity). Myristoylation at Gly-2 is required for membrane anchoring before palmitoylation. Palmitoylation at Cys-3 varies with membrane lipid composition. Belongs to the G-alpha family. G(i/o/t/z) subfamily.