Inserting a gene that controls human sleep habits into mice can transform the rodents into "early birds." This result provides insight into the molecular mechanisms that drive biological clocks.

Most organisms have an internal clock that synchronizes their activities to the 24-hour day--the so-called circadian rhythm. PER2 is one of the genes that controls this rhythm in humans. But in 0.3 percent of the population, the gene goes awry, causing familial advanced sleep phase syndrome (FASPS), which drives people early to bed and very early to rise. Despite causing such a striking effect, the change in the protein encoded by the mutant PER2 gene is quite subtle: a single protein building block, or amino acid, is changed from a serine to a glycine.

This article was originally published with the title Tinkering with Our Clock.

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