The goal of this proposal is to determine how the yeast """"""""two-component"""""""" regulator, Sln1p, controls the activity of the essential transcription factor Mcm1p. Sln1p has been characterized as the sensor-transmitter responsible for initial transduction of the osmotic stress signal through the Hog1p MAP kinase cascade. The authors have found that, additionally, Sln1p controls the activity of Mcm1p: activated sln1* mutations stimulate expression of the Mcm1p dependent reporter gene P-lacZ. Furthermore, regulation of Hog1p and Mcm1p define a branch point in the regulation conferred by Sln1p: both pathways were found to rely on Sln1p and the phosphorelay intermediate Ypd1p, but the signal diverges with the identity of the receiver molecule. Ssk1p is the receiver molecule for the Hog1p pathway and does not contribute to regulation of Mcm1p, whereas recent results from Dr. Fassler suggest that Skn7p is the likely receiver for the Mcm1p pathway. Accordingly, mutations in the downstream components of the Hog1p MAP kinase cascade have no effect on Mcm1p activity. Phenotypic analysis of the sln1* mutants reveals osmotic sensitivity indicating that the Hog1p and Mcm1p branches are reciprocally controlled by Sln1p phoshphorylation (increased phosphorylation results in concomitant osmotic sensitivity due to decreased signaling of Hog1p and increased Mcm1p activity). The authors intend to continue their analyses by: identifying and characterizing the factors mediating Sln1p control of Mcm1p; characterizing the biochemistry of Sln1p mediated signaling to Mcm1p; and characterizing the regions of Mcm1p required for response to the Sln1p signal.
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