As a consequence of the periodic light and dark cycles generated by the earth’s rotation, most organisms must regulate their behavior with daily periodicity. Rather than directly responding to light intensity and being subject to localized fluctuations such as a cloud passing overhead, many organisms anticipate light levels by keeping time with an internal circadian clock. Cyanobacteria are photosynthetic prokaryotes that have evolved an elegant circadian clock based on a post-transcriptional oscillator, and can keep time for days if the organism is moved to static light conditions. This oscillator modulates transcription of nearly all the organism’s genes with phases particular to different promoters, such that genes relevant to photosynthesis are transcribed during the day and genes for biological processes incompatible with oxygen are transcribed during the night.

I am studying the circadian phenomenon at the systems level using the cyanobacterium Synechococcus elongatus. By developing tools to globally monitor gene expression and the phosphorylation state of the post-transcriptional oscillator, we hope to answer questions about how the organism entrains its clock to the environment, and how expression patterns with different phases are generated.