CIRCADIAN-RHYTHMS IN RAPIDLY DIVIDING CYANOBACTERIA

The long-standing supposition that the biological clock cannot functio n in cells that divide more rapidly than the circadian cycle was inves tigated. During exponential growth in which the generation time was 10 hours, the profile of bioluminescence from a reporter strain of the c yanobacterium Synechococcus (species PCC 7942) matched a model based o n the assumption that cells proliferate exponentially and the biolumin escence of each cell oscillates in a cosine fashion. Some messenger RN As showed a circadian rhythm in abundance during continuous exponentia l growth with a doubling time of 5 to 6 hours. Thus, the cyanobacteria l circadian clock functions in cells that divide three or more times d uring one circadian cycle.