Ste5: a meeting place for MAP kinases and their associates.

Growth and differentiation of the budding yeast Saccharomyces cerevisiae is regulated by six functionally distinct but structurally similar MAP kinase cascades. Three of the protein kinases in the cascade that regulates G1-phase arrest and mating have recently been shown to form a multikinase complex with a LIM-domain-containing protein called Ste5. These studies implicate Ste5 as a tethering protein that physically links protein kinases operating sequentially in a cascade. The significance of this complex for the regulation and specificity of signal transduction is explored in this review.