ScienceDaily (Feb. 19, 2010) — A team of biologists has unraveled the biochemistry of how bacteria so precisely time cell division, a key element in understanding how all organisms from bacteria to humans use their biological clocks to control basic cellular functions.
"A major question in biology is how the circadian clock machinery is different in bacteria than it is in plants, animals and fungi," said Susan Golden, a professor of biology at UC Sana Diego, who headed the study. "We looked at how the biological clock controls when bacterial cells divide -- in bacteria, there's a period of four hours where the cells are not allowed to divide -- and we identified the structural changes in a key protein that controls this action."
Golden and her colleagues from UCSD, MIT, Michigan State University and Texas A&M University probed cell division in the cyanobacterium Synechococcus elongatus. That organism had been studied extensively by the Golden lab and other researchers, who found that the timing of cell division, patterns of gene expression and compaction of the chromosome are controlled by the circadian clock. What was unknown was precisely how the circadian clock in bacteria controlled cell division.
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Elevated ATPase Activity of KaiC Applies a Circadian Checkpoint on Cell Division in Synechococcus elongatus
Guogang Dong,Qiong Yang,Qiang Wang,Yong-Ick Kim,Thammajun L. Wood,Katherine W. Osteryoung,Alexander van Oudenaarden,Susan S. Golden
A circadian clock coordinates physiology and behavior in diverse groups of living organisms. Another major cyclic cellular event, the cell cycle, is regulated by the circadian clock in the few cases where linkage of these cycles has been studied. In the cyanobacterium Synechococcus elongatus, the circadian clock gates cell division by an unknown mechanism. Using timelapse microscopy, we confirm the gating of cell division in the wild-type and demonstrate the regulation of cytokinesis by key clock components. Specifically, a state of the oscillator protein KaiC that is associated with elevated ATPase activity closes the gate by acting through a known clock output pathway to inhibit FtsZ ring formation at the division site. An activity that stimulates KaiC phosphorylation independently of the KaiA protein was also uncovered. We propose a model that separates the functions of KaiC ATPase and phosphorylation in cell division gating and other circadian behaviors.
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