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AKB: Biologische Physik

AKB 40: Evolution and Complex Systems

AKB 40.3: Hauptvortrag

Donnerstag, 11. März 2004, 15:30–16:00, H40

Evolution of a Genetic Switch in a Fluctuating Environment — •Ulrich Gerland¹ and Terence Hwa² — ¹Sektion Physik, Uni München — ²Department of Physics, UC San Diego

Gene regulation encompasses a variety of molecular processes which determine the protein concentrations in cells and their signal dependence. Perhaps the simplest regulatory unit (or ‘node’ in a genetic network) is a genetic switch, which sets the transcription rate of a gene either to ‘high’ or ‘low’. Many genetic switches in bacteria respond to a chemical ‘inducer’ signaling the present state of a fluctuating environment. Mechanically, there are two basic designs, which are both realized in bacteria: either the transcription level is low by default and the inducer activates a DNA-binding protein stimulating transcription, or the inducer deactivates a DNA-binding protein repressing a high default level. We formulate a theory to quantitate an old evolutionary argument that attempts to rationalize the observed choice between these two designs in bacteria. To this end, we are forced to consider explicitly the effects of environmental fluctuations, which are usually neglected in standard evolutionary models.