Separate roles for N- and C-termini of the STE4 (β) subunit of the Saccharomyces cerevisiae G protein in the mediation of the growth arrest. Lack of growth-arresting activity of mammalian βγ complexes
✍ Scribed by Coria, Roberto; Ongay-Larios, Laura; Birnbaumer, Lutz
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 974 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0749-503X
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✦ Synopsis
Mating pheromone signal transduction in Saccharomyces cerevisiae involves a G protein composed to Scglp (Gpalp), Ste4p and Stel8p subunits, homologous to the a, and y subunits of mammalian G proteins. Growth arrest in G1 phase is activated by the Ste4plStel8p complex via a downstream pathway and it is negatively controlled by the Scglp subunit. Here we explored whether mammalian p or y subunits could functionally substitute for their yeast homologues. While no evidence was obtained for functional replacement of Ste4p and Stel8p, we found that overexpression of Stel8p potentiated the effect of hybrid proteins in which the N terminus of the Ste4p subunit was replaced by that of the mammalian p. 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 Stel8p, indicating that the truncated forms of Ste4p have retained their ability to form an active complex with Stel8p. 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 p subunit, indicating that the C terminus of Ste4p is essential to trigger the effector of the yeast pheromone response pathway.