MAPK pathway in <i>Saccharomyces Cerevisiae.</i>

<p>The MAPK pathway in <i>Saccharomyces cerevisiae</i> consists in a cascade of four successive kinases: Ste20, Ste11, Ste7 and a MAPK. In the results presented in the text, two MAPK are studied, Fus3 and Kss1. Activation of Kss1 has been recognized to be predominant during filamentation while Fus3 is relevant for the mating response. During mating, a scaffold protein, Ste5 is recruited to the membrane and bind to Ste11, Ste7 and Fus3. When activated, the Rho family protein cdc42, a small GTPase localized to the plasma membrane, binds and activates Ste20 through a CRIB domain. Ste20 remains at the plasma membrane. This point is the start of the cascade of reactions where a kinase activates the next kinase by phosphorylation. Ste20 activates the MAPK kinase kinase Ste11, which in turn activates a MAPK kinase, Ste7, which activates two different MAPKs, Kss1 and Fus3.