Control of Nitrogenase mRNA Levels by Products of Nitrate Assimilation in the Cyanobacterium Anabaena sp. Strain PCC 7120.

Nitrate inhibited nitrogenase synthesis and heterocyst development in the cyanobacterium Anabaena sp. strain PCC 7120. Inhibition of dinitrogen fixation by nitrate did not take place, however, in nitrate reductase-deficient derivatives of this strain. Hybridization of total RNA isolated from cells grown on different nitrogen sources with an internal fragment of the nifD gene showed that regulation of nitrogenase activity by nitrate is exerted through a negative control of the nitrogenase mRNA levels.