The Gbeta(KlSte4p) subunit of the heterotrimeric G protein has a positive and essential role in the induction of mating in the yeast Kluyveromyces lactis.
In the yeast Saccharomyces cerevisiae the Gbetagamma dimer of the heterotrimeric G protein transduces a pheromone signal from serpentine receptor to a MAP kinase cascade that activates the mating response pathway. Haploid cells lacking the Gbeta subunit do not respond to sexual pheromone, leading to sterility. In this work we demonstrate that the beta-subunit of Kluyveromyces lactis, encoded by the KlSTE4 gene, is a component of the G protein, and that its disruption gives rise to sterile cells. However, unlike Ste4p in S. cerevisiae, its overexpression does not induce growth arrest or promote mating. It has been shown that in K. lactis, the Galpha subunit has a positive role in the mating process, hence the resulting double GalphaDelta GbetaDelta mutant was viable and sterile. Here we show that the overproduction of Gbeta subunit fails to rescue GalphaDelta mutant from sterility and that expression of a constitutive active allele of Galpha enhances transcription of the KlSTE4 gene. The mating pathway triggered by the Gbeta-subunit requires a functional KlSte12p transcription factor. Gbeta has a 10-fold higher association rate with the Galpha1 subunit involved in pheromone response than with Galpha2, the protein involved in cAMP regulation in K. lactis. Additionally, the Gbeta-subunit from K. lactis is able to interact with the Galpha-subunit from S. cerevisiae but fails to restore the mating deficiency of Scste4Delta mutant. The data presented indicate that the mating pathway of K. lactis is positively and cooperatively regulated by both the Galpha and the Gbeta subunits.
Kawasaki
Laura
L
Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México. Apartado Postal 70-242. 04510 México, D.F., México.
Saviñón-Tejeda
Alma L
AL
Ongay-Larios
Laura
L
Ramírez
Jorge
J
Coria
Roberto
R
D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics / Q000378:metabolism; D044387:GTP-Binding Protein beta Subunits / Q000235:genetics / Q000378:metabolism*; D005800:Genes, Fungal; D007716:Kluyveromyces / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D010675:Pheromones / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013045:Species Specificity
D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D044387:GTP-Binding Protein beta Subunits; D010675:Pheromones; D029701:Saccharomyces cerevisiae Proteins; C067576:Ste4 protein, S cerevisiae