Separate roles for N- and C-termini of the STE4 (beta) subunit of the Saccharomyces cerevisiae G protein in the mediation of the growth arrest. Lack of growth-arresting activity of mammalian beta gamma complexes.
Mating pheromone signal transduction in Saccharomyces cerevisiae involves a G protein composed to Scg1p (Gpa1p), Ste4p and Ste18p subunits, homologous to the alpha, beta and gamma subunits of mammalian G protein. Growth arrest in G1 phase is activated by the Ste4p/Ste18p complex via a downstream pathway and it is negatively controlled by the Scg1p subunit. Here we explored whether mammalian beta or gamma subunits could functionally substitute for their yeast homologues. While no evidence was obtained for functional replacement of Ste4p and Ste18p, we found that overexpression of Ste18p potentiated the effect of hybrid proteins in which the N terminus of the Ste4p subunit was replaced by that of the mammalian beta. ste4 mutants having deletions in the N terminus showed a decreased activity in signalling to the downstream effector of the pheromone response. This defect was totally cured by overexpression of Ste18p, indicating that the truncated forms of Ste4p have retained their ability to form an active complex with Ste18p. Removal of six amino acids from the C terminus of Ste4p rendered a completely inactive subunit and this defect persisted in hybrids where the C terminus was placed by that of the beta subunit, indicating that the C terminus of Ste4p is essential to trigger the effector of the yeast pheromone response pathway.
Coria
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R
Departamento de Microbiología, Universidad Nacional Autónoma de México.
Ongay-Larios
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L
Birnbaumer
L
L
D000595:Amino Acid Sequence; D000818:Animals; D002455:Cell Division; D044387:GTP-Binding Protein beta Subunits; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D020962:Heterotrimeric GTP-Binding Proteins; D008322:Mammals; D000072235:Mating Factor; D008969:Molecular Sequence Data; D010455:Peptides / Q000502:physiology; D010675:Pheromones / Q000502:physiology; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013045:Species Specificity
D044387:GTP-Binding Protein beta Subunits; D010455:Peptides; D010675:Pheromones; D029701:Saccharomyces cerevisiae Proteins; C067576:Ste4 protein, S cerevisiae; D000072235:Mating Factor; D019204:GTP-Binding Proteins; D020962:Heterotrimeric GTP-Binding Proteins