Plasmids which contained the translational fusion ofEscherichia coli lacZ toRhodobacter capsulatus ferredoxin genes,fdxN andfdxA, were constructed. Effects of growth conditions on the expression of each ferredoxin were analyzed by measuring the β‐galactosidase activity inR. capsulatus which harbored a corresponding plasmid. TranscriptionfdxN::lacZ, the ferredoxin I fusion gene, was regulated at least 100‐fold by either NH+ 4 or O2 but not by illumination, confirming thatfdxN belongs to thenif‐gene family. Transcription offdxA::lacZ, the ferredoxin II fusion gene, however, was constant under all the conditions surveyed, suggesting that the protein has some constitutive function(s).
