CIRCADIAN CLOCKS IN PROKARYOTES

Prokaryotes have long been thought incapable of expressing circadian ( daily) rhythms. Recently, however, such biological 'clocks' have been discovered in several species of cyanobacteria. These endogenous timek eepers control gene expression on a global level in cyanobacteria. Eve n in cyanobacterial cultures that are growing with average doubling ti mes more rapid than one per 24 h, the circadian clock controls gene ex pression and cell division. We have isolated mutants of the cyanobacte rial circadian pacemaker and are currently characterizing the loci res ponsible for their altered period phenotypes.