CLONING, CHARACTERIZATION, AND REGULATION OF NIFF FROM RHODOBACTER-CAPSULATUS

The Rhodobacter capsulatus nifF gene and upstream sequence were cloned by using a probe based on the N-terminal sequence of NifP. nifF was f ound to not be contained in the previously described nif regions I, II , and III. Comparison of the deduced amino acid sequence showed that i t is highly similar to NifF from Azotobacter vinelandii and NifF from Klebsiella pneumoniae. Analysis of translational fusions demonstrated that the regulation of transcription was the same as previously report ed at the protein level. Insertional mutagenesis showed that NifF cont ributes significantly to nitrogenase activity under normal nitrogen-fi xing conditions and that it is absolutely required for nitrogen fixati on under iron limitation.