Kawasaki Laura, Saviñón-Tejeda Alma L, Ongay-Larios Laura, Ramírez Jorge, Coria Roberto
Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México. Apartado Postal 70-242. 04510 México, D.F., México.
Yeast. 2005 Sep;22(12):947-56. doi: 10.1002/yea.1278.
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.
在酿酒酵母中，异源三聚体G蛋白的Gβγ二聚体将来自蛇形受体的信息素信号传递至MAP激酶级联反应，从而激活交配反应途径。缺乏Gβ亚基的单倍体细胞对性信息素无反应，导致不育。在本研究中，我们证明了乳酸克鲁维酵母中由KlSTE4基因编码的β亚基是G蛋白的一个组成部分，其缺失会产生不育细胞。然而，与酿酒酵母中的Ste4p不同，其过表达不会诱导生长停滞或促进交配。研究表明，在乳酸克鲁维酵母中，Gα亚基在交配过程中起积极作用，因此产生的双Gα缺失Gβ缺失突变体是存活的但不育。在此我们表明，Gβ亚基的过量产生无法挽救Gα缺失突变体的不育性，并且Gα组成型活性等位基因的表达增强了KlSTE4基因的转录。由Gβ亚基触发的交配途径需要功能性的KlSte12p转录因子。与参与cAMP调节的Gα2相比，Gβ与参与信息素反应的Gα1亚基具有高10倍的结合速率。此外，乳酸克鲁维酵母的Gβ亚基能够与酿酒酵母的Gα亚基相互作用，但无法恢复Scste4Δ突变体的交配缺陷。所呈现的数据表明，乳酸克鲁维酵母的交配途径受到Gα和Gβ亚基的正向协同调节。
