The circadian clock

As you step off a trans-oceanic flight into the midday bustle of an airport, your body may be telling you that it's time for bed. This is because our body's sense of time depends as much on an internal clock as it does on external cues. Our internal clock – known as the circadian clock – will eventually synchronize itself with the new day–night cycle, but not before we suffer through the mind-deadening effects of jet lag. Reestablishing a link between the external clock (the sun) and our internal clock is essential for human health. Disruption of circadian rhythms has been linked to mania in people with bipolar disorder, and various health problems manifest themselves more often during the morning (heart attacks) or at night (asthma attacks) depending on our internal clock.

• Regulatory regions and sequence motifs

• Motif finding algorithms

• Combining expression and sequence data

The circadian clock is fundamental to many organisms. Bacteria, insects, fungi, mammals, and many other species maintain an internal clock in order to synchronize their metabolism, activity, and body temperature to the sun. In no other organism is the ability to keep time as important as it is in plants. Much more than in mobile species, plants depend on a steady day–night cycle for energy production: they are able to photosynthesize sunlight during the day to store energy, but must use up these stores at night.