The DNA sequence of the Rhodobacter capsulatus ntrA, ntrB and ntrC gene analogues required for nitrogen fixation.

We have determined the DNA sequence for the genes nifR1, nifR2 and nifR4 in the photosynthetic bacterium Rhodobacter capsulatus. These genes regulate transcription of the nifHDK operon and so limit the expression of nitrogen fixation activity to periods of low environmental concentrations of both oxygen and fixed nitrogen. The sequences of these three genes are similar to components of the ntr regulation system in Escherichia coli and Klebsiella pneumoniae. The two-component regulatory system of ntrB and ntrC in E. coli is represented by nifR2 and nifR1 in R. capsulatus and nifR4 in R. capsulatus is the equivalent of the E. coli ntr-related sigma factor ntrA.