CHARACTERIZATION OF THE RHYTHMIC NITROGEN-FIXING ACTIVITY OF SYNECHOCOCCUS SP RF-1 AT THE TRANSCRIPTION LEVEL

Synechococcus RF-1 synthesizes mRNA for nitrogenase continuously when the culture is growing in continuous light. The synthesis of the nitrogenase mRNA is cyclic and occurs exclusively during the dark periods when the culture grows in a diurnal light/dark regimen. Nif gene expression continues to take place in a cyclic pattern after the culture is transferred from a diurnal light/dark regimen to continuous light. The cyclic synthesis of mRNA for nitrogenase can be induced in a continuous light culture by periodic exposure of the culture to 3(3,4-dichlorophenol)-1,1-dimethylurea. Although Ca++ is necessary for the expression of nitrogenase activity in Synechococcus RF-1 in vivo, the results of Northern blot assays indicate that the role of Ca++ is not at the transcription level. © 1990 Springer-Verlag New York Inc.