The Gβ(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 Gβγ 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 Gβ subunit do not respond to sexual pheromone, leading to sterility. In this work we demonstrate that the β‐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 Gα subunit has a positive role in the mating process, hence the resulting double GαΔ GβΔ mutant was viable and sterile. Here we show that the overproduction of Gβ subunit fails to rescue GαΔ mutant from sterility and that expression of a constitutive active allele of Gα enhances transcription of the KlSTE4 gene. The mating pathway triggered by the Gβ‐subunit requires a functional KlSte12p transcription factor. Gβ has a 10‐fold higher association rate with the Gα1 subunit involved in pheromone response than with Gα2, the protein involved in cAMP regulation in K. lactis. Additionally, the Gβ‐subunit from K. lactis is able to interact with the Gα‐subunit from S. cerevisiae but fails to restore the mating deficiency of Scste4Δ mutant. The data presented indicate that the mating pathway of K. lactis is positively and cooperatively regulated by both the Gα and the Gβ subunits. Copyright © 2005 John Wiley & Sons, Ltd.