Circadian programming in cyanobacteria

Prokaryotic cyanobacteria express robust circadian (daily) rhythms under the control of a timing mechanism that is independent of the cell division cycle. This biological clock orchestrates global regulation of gene expression. Competition experiments demonstrate that fitness is enhanced when the circadian period is consonant with the period of the environmental cycle. Multational analyses have identified three clock genes in the organism, one of which is related to DNA recombinases and helicases. We propose a new model for the Corp 'clockwork' that implicates rhythmic changes in the status of the chromosome that underly the rhythms of gene expression.