The Death of a Gene

When a gene is duplicated, the new copy is often dead-on arrival (lacks the regulatory elements). 

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#Unit 4. Cell Communication and Cell Signaling

An a haploid cell secretes the a mating factor and has GPCRs for the α factor on its cell surface; an α cell secretes the α factor and has GPCRs for the a factor.

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#Unit 4. Cell Communication and Cell Signaling

Activation of the MAP kinase pathway by either the a or the α GPCRs induces transcription of genes that inhibit progression of the cell cycle

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#Unit 4. Cell Communication and Cell Signaling

The receptors for yeast α and a mating factors are coupled to the same trimeric G protein.

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#Unit 4. Cell Communication and Cell Signaling

Ligand binding to either of the two yeast pheromone GPCRs triggers the exchange of GTP for GDP on the Gα subunit and dissociation of Gα∙GTP from the Gβγ complex.

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#Unit 4. Cell Communication and Cell Signaling

Ligand binding and dissociation of the G protein subunits, the membrane-tethered Gβγ subunit binds the Ste5.

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#Unit 4. Cell Communication and Cell Signaling

Ste5 acts as a scaffold for assembling other components in the cascade Ste11, Ste7, and Fus3.