Function of the STE4 and STE18 Genes in Mating Pheromone Signal Transduction in Saccharomyces cerevisiae

Abstract

Many cell-surface receptors are coupled to intracellular effectors through a guanine-nucleotide-binding (G) protein. For example, the G protein transducin couples the visual pigment rhodopsin to an intracellular cGMP phosphodiesterase and therefore allows externally detected photons to modulate intracellular levels of cGMP. The G proteins Gi and Gs couple external levels of inhibitory agents, such as α2-adrenergic and muscarinic agonists, and stimulatory agonists, such as epinephrine, to adenylate cyclase; thus, these agonists can regulate cAMP levels within the cell (for review, see Stryer and Bourne 1986; Gilman 1987; Neer and Clapham 1988). All of these various G proteins have similar structures. They are heterotrimers of subunits designated α, α, and γ. The α subunits are variable in primary sequence and serve to define the specific G proteins. They range in size from 40 kD, for the α subunit of the transducin specific for retinal rods, to 52 kD for Gsα (Gilman...