The Gβ(KISte4p) 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 G beta gamma 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 Go 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 KISTE4 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 Ga subunit has a positive role in the mating process, hence the resulting double G alpha Delta G beta A Delta mutant was viable and sterile. Here we show that the overproduction of G beta subunit fails to rescue G alpha Delta mutant from sterility and that expression of a constitutive active allele of Got enhances transcription of the KISTE4 gene. The mating pathway triggered by the G beta-subunit requires a functional KISte12p transcription factor. G beta has a 10-fold higher association rate with the Gal subunit involved in pheromone response than with Gal, the protein involved in CAMP regulation in K. lactis. Additionally, the G beta-subunit from K. lactic is able to interact with the Get-subunit from S. cerevisiae but fails to restore the mating deficiency of Scste4 Delta mutant. The data presented indicate that the mating pathway of K. lactis is positively and cooperatively regulated by both the G alpha and the G beta subunits. Copyright (c) 2005 John Wiley & Sons, Ltd.