| The calcineurin phosphatase mediates stress response in organisms as diverse as mammals, where it activates the immune system, and the pathogenic microbe C. neoformans, where it is essential for survival in the host. To survive ionic, pH, and pheromone stress, the yeast Saccharomyces cerevisiae activates signaling through this Ca 2+ activated serine/threonine phosphatase calcineurin to the transcription factor Crz1p/Tcn1p. We show that the overexpression of SKN7, a response-regulator transcription factor, activates transcription from a calcineurin/Crz1p dependent response element (CDRE). Ca2+-induced, calcineurin/Crz1p-dependent activation of several genes is reduced in a skn7 mutant. Skn7p modulates CDRE dependent transcription by affecting Crz1p protein levels. Specifically, the rate of Crz1p turnover is increased in skn7 mutants. Calcineurin, but not its phosphatase activity, is required for Skn7p-mediated Crz1p stabilization. Skn7p binds to both calcineurin and Crz1p in vitro, and we suggest that this interaction is required for Skn7p regulation of Crz1p.; The DNA binding domain and an internal coil-coil domain, but not the response-regulator phosphorylation site of Skn7p, are necessary for Crz1p-dependent transcriptional activation and Crz1p stabilization by Skn7 in vivo . The DNA binding domain of Skn7p is also required for binding to Crz1p and calcineurin in vitro. Thus, we propose that Skn7p protects Crz1p from degradation by binding to it and calcineurin through its DNA binding domain. This characterization of Skn7p is novel in several key regards. First, we implicate the response-regulator transcription factor Skn7p in the regulation of protein stability. Second, we characterize a phosphatase-independent role for the calcineurin enzyme. Lastly, we implicate the Skn7p DNA binding domain in the mediation of protein-protein interactions. |
