A circadian rhythm is the daily rhythmic activity cycle, based on 24-hour intervals, that is exhibited by many organisms. Bioluminescence from a firefly is created by an enzymatic reaction that takes place in its abdomen. The enzyme responsible for this light-producing reaction is called luciferase. Luciferase uses oxygen, ATP and luciferin to generate light. The firefly's DNA contains the genetic information for the enzyme luciferase. The luciferase gene is the blueprint that an organism uses to make the luciferase protein. The DNA encoding the luciferase gene can be introduced into the genetic makeup of the other organisms. Dr. Steve A. Kay, from the Scripps Research Institute has introduced the gene into fruit flies, plants and bacteria. Once these genetically altered organisms contain the gene for luciferase, they can glow in the dark. Organisms regulate their behavior and metabolism in a circadian cycle. Examples of this are a human's sleep/wake cycle or a flower's open/close cycle. The cycles are controlled by an internal circadian clock that resides within our cells. Dr. Kay's laboratory utilizes luciferase bioluminescence technology to observe what happens inside these clocks.