As fig a15 shows g g transmits the signal initiated by

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Unformatted text preview: turns on genes involved in G1 arrest of cells, cell fusion, and nuclear fusion. Mutations in genes in any of these pathways cause defects in mating. As Fig. A.15 shows, G / G transmits the signal initiated by pheromone binding through a series of three protein kinases, known collectively as a MAP kinase cascade. In the pheromone response pathway, the trio of kinases first phosphorylate each other and then promote phosphorylation of the Dig1 and Dig2 proteins which inhibit the STE12 gene product. Phosphorylation of Dig1/Dig2 causes them to release Ste12, the transcription factor. Since transcription occurs in the nucleus, the activation of Ste12 shows that the signal transduction pathway has transduced the pheromone-induced signal from the plasma membrane to the nucleus. Ste12 activates the transcription of several genes whose products contribute to cell fusion (for example, FUS1) and nuclear fusion (for example, KAR5). All these processes are necessary for mating. Components of the ty...
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