Graduate Program in Biophysical Sciences, The University of Chicago, Chicago, United States; Department of Chemistry, The University of Chicago, Chicago, United States; James Franck Institute, The University of Chicago, Chicago, United States
Graduate Program in Biophysical Sciences, The University of Chicago, Chicago, United States; Department of Ecology and Evolution, The University of Chicago, Chicago, United States; Department of Molecular Genetics and Cell Biology, The University of Chicago, Chicago, United States; Department of Physics, The University of Chicago, Chicago, United States
Circadian rhythms are biological oscillations that schedule daily changes in physiology. Outside the laboratory, circadian clocks do not generally free-run but are driven by daily cues whose timing varies with the seasons. The principles that determine how circadian clocks align to these external cycles are not well understood. Here, we report experimental platforms for driving the cyanobacterial circadian clock both in vivo and in vitro. We find that the phase of the circadian rhythm follows a simple scaling law in light-dark cycles, tracking midday across conditions with variable day length. The core biochemical oscillator comprised of the Kai proteins behaves similarly when driven by metabolic pulses in vitro, indicating that such dynamics are intrinsic to these proteins. We develop a general mathematical framework based on instantaneous transformation of the clock cycle by external cues, which successfully predicts clock behavior under many cycling environments.
