CPLC/iPoLS Seminar: Catherine Ann Royer, Rensselaer Polytechnic Institute "Molecular mechanisms of size control in budding yeast"

The fundamental question of how a cell knows it has grown large enough to divide has remained unanswered for decades. The balance between growth and division underlies cellular homeostasis and fitness of unicellular organisms. It defines the size of organs in higher eukaryotes and is strongly deregulated in many disease states, most notably cancer. Despite its importance and a wealth of genetic studies in budding yeast defining factors implicated in size control, the underlying molecular mechanisms have remained a mystery. To begin to define these mechanisms we have used a combination of yeast genetics, advanced single molecule and fluctuation microscopy approaches, as well as mathematical modeling. We have discovered an underlying biochemical titration of the G1/S promoter target sites by the G1/S transcriptional activators. Moreover we show that these activators are upregulated in poor nutrients, providing a molecular explanation for nutrient control of cell size.