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The most impressive clocks can’t be found on a phone, wristband, or wall. These timepieces are hidden inside cells, where they tick along naturally recurring (circadian) rhythms, alerting the cell when it’s time to express various genes. Erin O’Shea’s research has examined the circadian clock found in blue-green algae, or cyanobacteria.

O’Shea and colleagues have shown how a master transcription factor, RpaA, triggers an entire cascade of circadian gene expression by regulating a set of transcription factors known as sigma factors. The genes controlled by RpaA and the sigma factors help the bacterial cell sustainably generate the energy compound ATP by regularly shifting its metabolism between daytime photosynthesis and nighttime use of stored carbon sources, such as glycogen.

In other work, O’Shea and collaborators have analyzed how cells make the most of a limited number of transcription factor proteins, through their dynamics. You can interpret your friend’s words in different ways, by listening to her delivery. Similarly, O’Shea’s team has shown, the control regions of genes can interpret a transcription factor’s signal based on its communication style – steady, pulsing, shorter or longer, etc. Decoding these dynamics, the DNA identifies the signal and activates the correct gene(s).