Yeast Mating Type

Abstract

Yeast mating type is determined by alleles of a single genetic locus that encodes regulatory proteins governing genes encoding mating pheromones, pheromone receptors and downstream effectors regulating cell type. Some yeast are capable of switching mating type, a process involving gene replacement by information from silenced copies of the mating type locus found elsewhere in the genome.

Keywords: mating type; sterile mutants; mating type switching; cell cycle; signal transduction

Figure 1.

Genes active at the mating type locus in a or α haploids, or in a/α diploids. The different colours indicate that there is a portion of this locus that is not the same in the two mating types. (a) In mating type a cells, the MATa1 gene is expressed. a‐specific genes are expressed by a default pathway; α‐specific genes are not expressed; haploid‐specific genes are expressed by default pathways; and one of the haploid‐specific genes is a repressor of meiosis. (b) In mating type α cells, the MATα1 and MATα2 genes are both expressed. The former is an activator of α‐specific genes and the latter a repressor of a‐specific genes. Haploid‐specific genes are expressed, including the repressor of meiosis. (c) When both alleles are present in an a/α diploid, MATα2 protein continues to repress a‐specific genes as in (b), and interacts with the product of MATa1 to repress the haploid‐specific genes and allow meiosis and sporulation.

Figure 2.

Signal transduction pathway for response to mating pheromone. Mating pheromone is an extracellular peptide that interacts with the extracellular portion of the appropriate transmembrane receptor (Ste2 or Ste3 protein). Binding of pheromone to receptor causes a conformational change in the associated G protein, which consists of three subunits (Gα, product of the GPA1 gene, Gβ, product of STE4 and Gγ, product of STE18). This conformational change results in dissociation of the Gβ and Gγ subunits, which activates Ste20 protein, a protein kinase. Ste20p phosphorylates the mitogen‐activated protein (MAP) kinase kinase kinase (MAPKKK), Ste11p. This in turn phosphorylates the MAP kinase kinase (MAPKK) Ste7p, which phosphorylates the MAP kinase (Fus3p). Fus3p phosphorylates target proteins that regulate the cell cycle or activate transcription of genes required for mating.

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References

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Further Reading

Gustin MC, Albertyn J, Alexander M and Davenport K (1998) MAP kinase pathways in the yeast Saccharomyces cerevisiae. Microbiology and Molecular Biology Reviews 62: 1264–1300.

Hartwell LH (1993) Getting started in the cell cycle. In: Hall MN and Linder P (eds) The Early Days of Yeast Genetics, pp. 307–314. Plainview, NY: Cold Spring Harbor Laboratory Press

MacKay VL (1993) a's, α's, and shmoos: mating pheromones and genetics. In: Hall MN and Linder P (eds) The Early Days of Yeast Genetics, pp. 273–290. Plainview, NY: Cold Spring Harbor Laboratory Press.

Oshima Y (1993) Homothallism, mating‐type switching, and the controlling element model in Saccharomyces cerevisiae. In: Hall MN and Linder P (eds) The Early Days of Yeast Genetics, pp. 291–304. Plainview, NY: Cold Spring Harbor Laboratory Press.

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Montelone, Beth A(Mar 2003) Yeast Mating Type. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000598]