Synthetic oligonucleotides, which were designed according to amino acid sequences conserved between and DraT and DraG, respectively, were used to identify the corresponding genes of Sequence analysis of a 1904 bp DNA fragment proved the existence of and These two genes were separated by 11 bp only, suggesting that and were part of one transcriptional unit. In contrast to and , the genes were not located upstream of the structural genes of nitrogenase but close to the gene at a distance of about 1000 kb from the genes. Deletion mutations in the gene region were constructed and introduced into wild-type and a deletion strain. The resulting mutant strains were examined for post-translational regulation of the molybdenum and the alternative nitrogenase in response to ammonia and darkness. Under ‘switch-off’ conditions the modified (ADP-ribosylated) and the non-modified forms of component II of both the molybdenum and the alternative nitrogenase were detected in a wild-type background by immunoblot analysis, whereas only the non-modified forms were present in the deletion strains. Nitrogenase activity in these strains was followed by the acetylene reduction assay. In contrast to the wild-type, mutants were not affected in nitrogenase activity in response to ammonia or darkness. These results demonstrated that the genes are required for post-translational regulation of both the molybdenum and the heterometal-free nitrogenase in


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