| Modification Notes |
Heterotrimeric G proteins function to relay information from cell surface receptors to intracellular effectors. Each of a very broad range of receptors specifically detects an extracellular stimulus (i.e. a photon, pheromone, odorant, hormone or neurotransmitter), while the effectors (e.g. adenyl cyclase), which act to generate one or more intracellular messengers, are less numerous. In mammals, G protein å, ∫ and © polypeptides are encoded by at least 16, 4 and 7 genes, respectively. Most interest in G proteins has been focused on their a subunits, since these proteins bind and hydrolyze GTP and most obviously regulate the activity of the best studied effectors. Evidence, however, has established an important regulatory role for the ∫© subunits. It is becoming increasingly clear that different G protein complexes expressed in different tissues carry structurally distinct members of the © as well as the å and ∫ subunits, and that preferential associations between members of subunit families increase G protein functional diversity. |