INFORMATION TRANSMISSION AND GRADIENT SENSING IN THE Saccharomyces cerevisiae PHEROMONERESPONSE PATHWAY

ALEJANDRO COLMAN LERNER; ALAN BUSH; ALEJANDRA VENTURA; ARIEL CHERNOMORETZ

Potrero de los Funes, San Luis

Congreso; SAIB 47th Annual Meeting Argentine Society for Biochemistry and Molecular Biology XLVII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2011

Society for Biochemistry and Molecular Biology XLVII Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

We studied the quantitative behavior of a prototypical information sensing and decision-making system, the mating pheromone response pathway in yeast. To locate a partner, yeast measure external mean concentration and direction of the pheromone gradient. To study concentration determination, we used fluorescent protein fusions, and monitored signal propagation in single cells with seconds to minutes time resolution. We quantified by microscope-based cytometry membrane recruitment of the MAP kinase cascade scaffold Ste5 and activation of the transcription factor Ste12. We found that this system relays information precisely and that this behavior relies on negative feedback originating on the MAP kinases. For gradient determination, yeast measures on which side there are more bound receptors. This sensing modality only works in non-saturating concentrations. However, yeast orient in the direction of the gradient even in very high external average concentrations. Surprisingly, our numerical simulations show that the slow binding dynamics of pheromone to its receptor enhances gradient determination in saturating conditions, resulting in more precise polarizations than comparatively faster binding rates. Our results show that eukaryotic systems employ system level regulatory mechanisms to ensure faithful information transmission even in saturating conditions.