Identification and characterization of the nifH and nifJ promoter regions located on the nif-plasmid pEA3 of Enterobacter agglomerans 333.

Small restriction fragments of the plasmid-borne Enterobacter agglomerans 333 nif region were cloned into a promoter probe plasmid as transcriptional fusions with the lacZ gene. Identification of NifA-dependent promoters was accomplished by using a compatible plasmid which constitutively expresses the Klebsiella pneumoniae nifA gene. beta-Galactosidase assays showed strong activation of the cloned E. agglomerans promoters in Escherichia coli by the heterologous K. pneumoniae nifA gene product. The positions of the promoter fragments on the corresponding restriction map were determined by Southern hybridization. As confirmed by sequencing data, the nifH and nifJ promoters are situated at opposite end-points of the nif gene group and their -24 to -12 nucleotide sequences are similar to the consensus sequence of NtrA-dependent promoters. Also, typical NifA-binding motifs are present in both promoters. The agreement of the promoter proximal regions of nifH and nifJ with the corresponding K pneumoniae sequences is about 80%. Also the upstream regions of these genes are in agreement to some extent.