Three genes essential to circadian rhythms in cyanobacteria, the simplest organisms known to have such "internal clocks," have been identified by scientists funded by the National Science Foundation (NSF). The research, by biologists Carl Johnson of Vanderbilt University and Susan Golden of Texas A & M University, is published in this week's issue of Science.
"Circadian rhythms enable organisms to react to the two most predictable events on Earth -- day and night," said Shil DasSarma, program manager in NSF's division of molecular and cellular biosciences, which funded the research. The clocks that power circadian rhythms are complex mechanisms of chemical reactions that control the timing of events in cells.
To identify genes involved in the circadian rhythm process, the researchers used a gene for a bioluminescent enzyme to indicate the activity of another gene that they knew the circadian clock controlled. Whenever the circadian clock was working, the cell made bioluminescent proteins rhythmically-causing the cell to glow with a predictable pattern throughout the day. This made it easier for researchers to identify which cyanobacteria had working circadian clocks, since they were the ones glowing like fireflies.
Once they could spot cyanobacteria without such clocks, or whose clocks did not keep the correct time, the researchers could find which genes were not functioning properly. What they found was a cluster of three genes, which they named kaiABC, after the Japanese word for cycle, "kai". KaiABC contains the information that the cell will use to make proteins called KaiA, B and C, respectively. The Kai proteins, they theorize, are integral components of the feedback loop that drives the circadian clock.
"The expression of KaiC is critically important for setting the phase of
the clock," said Golden. The researchers found that the levels of kaiC gene
expression increase during daytime and de
Contact: Greg Lester
National Science Foundation