Disease relevance of nifH

• Two other clusters included bacteria showing similarity with the genera Methylobacterium and Burkholderia, and amplification with primers for nifH and/or nodC regions was achieved with these strains [1].
• In Rhizobium japonicum the nitrogenase genes nifH and nifDK are separated [2].
• In contrast to Klebsiella pneumoniae or fast-growing Rhizobium species, such as R. meliloti, where the nitrogenase structural genes are clustered in one operon (nifHDK), in slow-growing Rhizobium japonicum 110, nifH and nifDK are on separate operons [2].
• DNA fragments containing either the nifD or nifH promoter and 5' structural gene sequences from Bradyrhizobium japonicum I110 were fused in frame to the lacZ gene [3].
• Characterization of an Azospirillum brasilense Tn5 mutant with enhanced N(2) fixation: the effect of ORF280 on nifH expression [4].

High impact information on nifH

• Deletion of the UASs in front of the nifH gene not only reduced the expression of nifH down to 2.5% but, surprisingly, also resulted in a reduction of the fixB mRNA level to less than 20% [5].
• This is in clear contrast to the situation with nifH and nifD promoters [6].
• The region upstream of nifH was characterized further by DNA sequence analysis and was shown to contain the nifB gene [7].
• No nif-positive regulatory mutants were identified from among an array of Fix- mutants in which Tn5 was inserted 9 kilobase pairs upstream of the nifDK operon and within the 18-kilobase-pair region separating the nifDK and nifH operons [3].
• This paper presents a phylogenetic comparison of a nitrogen fixation gene (nifH) with the aim of elucidating the processes underlying the evolutionary history of Rhodopseudomonas palustris [8].

Biological context of nifH

• The nifH and nifDK promoter regions from Rhizobium japonicum share structural homologies with each other and with nitrogen-regulated promoters from other organisms [9].
• Expression of the B. japonicum NifA from the hybrid nptII-nifH promoter (plasmid pBPF204) induced "in trans" lacZ transcription from the Azotobacter chroococcum nifH promoter in E. coli and A. diazotrophicus cells grown at low pO2 [10].
• These results strongly suggest that the nifH of Rps. palustris is highly related to those of the phototrophic purple non-sulfur bacteria included in this study, and might have come from an ancestral gene common to these phototrophic species through lateral gene transfer [8].

Analytical, diagnostic and therapeutic context of nifH

• Sequence analysis of the DNA showed a consensus promoter region upstream for the nifH gene containing a -24/-12 type promoter together with NifA- and integration host factor (IHF)- binding sites [11].
• The close association of the strains of Rps. palustris with those of Rhodobacter and Rhodovulum, as well as Rhodospirillum rubrum, was supported by the mol% G+C of their nifH gene and by the signature sequences found in the sequence alignment [8].
• Western blot analyses of tissue from the same nodules detected 32% the level of dinitrogenase and 31% the level of dinitrogenase reductase in L2-110 relative to MN-110 [12].
• Interestingly, Northern blot analyses revealed that L2-110 nodules, despite their lack of symbiotic nitrogen fixation, contained 65% the level of mRNA for dinitrogenase (nif DK) and 64% the level of dinitrogenase reductase (nif H) mRNA relative to MN-110 nodules [12].

References