BIOLOGICAL CLOCK IN THE PROKARYOTE SYNECHOCOCCUS RF-1

The prokaryote Synechococcus RF-1 exhibits circadian rhythms of nitrogen fixation and leucine uptake after being entrained in a diurnal light/dark regimen. The rhythms can also be established by small temperature changes, in either a raised- or a lowered-temperature cycle, within the growth-permissive range. At the biochemical level, the circadian oscillator in Synechococcus RF-1 controls, in addition to the nitrogenase, the synthesis rate at which more than ten polypeptides are synthesized. At the physiological and the biochemical levels, the overt rhythms have fixed phase relationships, though the phase is dependant on the particular induction stimuli. A ''clock'' consisting of a molecular complex which can respond differentially to different induction conditions is hypothesized.