INFORMATION TRANSMISSION AND GRADIENT SENSING IN THE Saccharomyces cerevisiae PHEROMONE RESPONSE PATHWAY

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

Potrero de los Funes, San Luis

Conferencia; 47 Annual Meeting Argentine Society for Biochemistry and Molecular Biology; 2011

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

We studied the quantitative behavior of a prototypical informationsensing and decision-making system, the mating pheromoneresponse pathway in yeast. To locate a partner, yeast measureexternal mean concentration and direction of the pheromonegradient. To study concentration determination, we usedfluorescent protein fusions, and monitored signal propagation insingle cells with seconds to minutes time resolution. We quantifiedby microscope-based cytometry membrane recruitment of theMAP kinase cascade scaffold Ste5 and activation of thetranscription factor Ste12. We found that this system relaysinformation precisely and that this behavior relies on negativefeedback originating on the MAP kinases. For gradientdetermination, yeast measures on which side there are more boundreceptors. This sensing modality only works in non-saturatingconcentrations. However, yeast orient in the direction of thegradient even in very high external average concentrations.Surprisingly, our numerical simulations show that the slow bindingdynamics of pheromone to its receptor enhances gradientdetermination in saturating conditions, resulting in more precisepolarizations than comparatively faster binding rates. Our resultsshow that eukaryotic systems employ system level regulatorymechanisms to ensure faithful information transmission even insaturating conditions.