A 2-COMPONENT SYSTEM THAT REGULATES AN OSMOSENSING MAP KINASE CASCADE IN YEAST

IN the prokaryotic two-component signal transduction systems, recognition of an environmental stimulus by a sensor molecule results in the activation of its histidine kinase domain and phosphorylation of a histidine residue within that domain(1-3). This phosphate group is then transferred to an aspartate residue in the receiver domain of a cognate response regulator molecule, resulting in the activation of its output function. Although a few eukaryotic proteins were identified recently that show sequence similarity to the prokaryotic sensors or response regulators, it has not been clear whether they constituted a part of a 'two-component' system(4-7). Here we describe a two-component system in Saccharomyces cerevisiae that regulates an osmosensing MAP kinase cascade(8,9).