7 Mar 2014
Michael Springer
Department of Systems Biology
Harvard Medical School
The response of yeast to galactose is one of the best-studied Eukaryotic signaling pathways. Glucose, the preferred carbon source, inhibits the utilization of galactose. Surprisingly, we have found that instead of simply inhibiting galactose utilization when glucose is above a threshold concentration, individual cells respond to the ratio of glucose and galactose and based on this ratio determine whether to induce genes involved in galactose metabolism. I will discuss how ratio sensing can arise, variation in quantitative details of galactose signaling we find between different strains, the genetic source of this variation, and the consequences on fitness. Time permitting, I will also discuss a screen we performed searching for mutants that effect the quantitative response to glucose and galactose and attempt to reconcile the disparate aspects we find between our mutant screen and natural variation.