Afr1p mediates activation of the Slt2p MAP kinase induced by pheromone, heat shock and hypo-osmotic shock in Saccharomyces cerevisiae.

In this study, we reinvestigated the role of Afr1p in the regulation of pheromone signaling and demonstrated that pheromone signaling was not regulated by Afr1p because neither deletion nor overexpression of AFR1 affected alpha-factor-induced transcription induction of the FUS1 gene. The enhanced alpha-factor resistance resulting from overexpression of AFR1 was dependent on the Slt2p mitogen-activated protein kinase. We also found that alpha-factor-induced activation of Slt2p required Afr1p. In the absence of Afr1p, activation of Slt2p was significantly reduced and, in a strain overexpressing Afr1p, the level of Slt2p activation was enhanced, indicating that Afr1p may function to mediate cross-talks between the mating pathway and the cell integrity pathway. Further, Afr1p was also required for adequate activation of Slt2p in cells exposed to heat shock and hypo-osmotic shock. These results indicated that, in addition to its role in establishing pheromone-induced morphogenesis, Afr1p may act as a 'sensor' to transduce cell wall stress resulting from different stimuli to the cell integrity pathway, leading to Slt2p activation.

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