Probing Chemical Time-Keeping

Our internal clocks may be a pain for frequent flyers dealing with jetlag, but the time-keeping helps us regulate metabolism so that we efficiently use energy when we are awake or asleep. Now researchers based in the U.K. are reporting that such cellular time-keeping—also known as circadian rhythms--involves a previously unknown cycle of posttranslational modifications, in addition to the transcription of a well-known handful of clock genes. Better understanding of circadian rhythms may help scientists optimize the efficiency of cellular metabolism and allow them to, for example, engineer better biofuel-producing algae and monitor metabolic diseases such as diabetes.

According to Akhilesh B. Reddy at the University of Cambridge, Andrew J. Millar at the University of Edinburgh, and coworkers, cellular time-keeping involves a repetitive sequence of oxidations and reductions of a cysteine thiol on a peroxiredoxin protein (Nature, DOI: 10.1038/nature09654; DOI:10.1038/nature09702). The team showed that circadian rhythms are maintained without transcription in red blood cells—which don't have a nucleus and therefore can't transcribe—and in a model algae in which transcription had been turned off with a chemical inhibitor.

"The research is provocative and inventive," says Joseph Bass, a medical researcher at Northwestern University. The field of circadian rhythms "has been shaped by genetic discoveries. The work opens up new questions concerning the origins and functions of molecular clocks."