The cyclic synthesis of the nitrogenase ofSynechococcusRF-1 and its control at the transcription level

In a diurnal light/dark regimen Synechococcus RF-1 fixes N2 at a high rate but almost exclusively during the dark periods. Studying the time course of nitrogenase synthesis by using chloramphenicol and nitrate revealed that re-initiation of nitrogenase synthesis was required for nitrogen fixation to appear during the dark period. Northern blot analysis demonstrated that nitrogenase-specific mRNA expressed itself only in the dark for a culture growing in a diurnal light/dark regimen The results proved that the nitrogenase of Synechococcus RF-1 is synthesized cyclically when the organism is growing in a diurnal light/dark regimen and that this cyclic synthesis is controlled at the transcription level.