Precise circadian clocks in prokaryotic cyanobacteria.

Cyanobacteria exhibit robust circadian rhythms controlled by a timing mechanism independent of the cell division cycle.

• The biological clock regulates global gene expression and the timing of cell division.
• Three clock genes organized as a gene cluster have been identified through mutational screening.
• Rhythmic changes in chromosome status may underlie the observed rhythms of gene expression.
• Mixed-strain experiments suggest that this timing mechanism may provide adaptive advantages during competition.

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