The Rhizobium etli gene iscN is highly expressed in bacteroids and required for nitrogen fixation

Abstract

Sequence analysis of the rpoN (2)- fixA intergenic region in the genome of Rhizobium etli CNPAF512 has uncovered three genes involved in nitrogen fixation, namely nifU, nifS and nifW. These genes are preceded by an ORF that is highly conserved among nitrogen-fixing bacteria. It encodes a putative gene product of 105 amino acids, belonging to the HesB-like protein family. A phylogenetic analysis of members of the HesB-like protein family showed that the R. etli HesB-like protein clusters with polypeptides encoded by ORFs situated upstream of the nifUS nitrogen fixation regions in the genomes of other diazotrophs. The R. etli ORF that encodes the HesB-like protein was designated iscN. iscN is co-transcribed with nifU and nifS, and is preferentially expressed under free-living microaerobic conditions and in bacteroids. Expression is regulated by the alternative sigma factor RpoN and the enchancer-binding protein NifA. A R. etli iscN mutant displays a reduction in nitrogen fixation capacity of 90% compared to the wild-type strain. This Nif(-) phenotype could be complemented by the introduction of intact copies of R. etli iscN.

Systems biology of bacterial nitrogen fixation: High-throughput technology and its integrative description with constraint-based modeling

“…Furthermore, the iscN mutant in R. etli showed a significant reduction in nitrogen fixation [35]. Consistent with this report, in silico gene deletion analysis of those genes codifying for nitrogenase mostly reduces nitrogen fixation, see Figure 3.…”

IscR‐dependent gene expression links iron‐sulphur cluster assembly to the control of O2‐regulated genes in Escherichia coli

“…However, three new genes of unknown function ( yabI , yadR and yhgI ) were identified as candidates for repression by IscR specifically under anaerobic conditions. YabI is a predicted inner membrane protein, while both YadR and YhgI are in the HesB/YadR/YfhF protein family (Dombrecht et al ., 2002) of which IscA (formerly known as YfhF) is also a member. Complementation studies have also implicated YhgI (also called GntY) and YhgH (GntX), encoded directly upstream of yhgI , in gluconate uptake (Porco et al ., 1998); however, a direct role for YhgI alone in this process was not tested.…”

The NifA-RpoN Regulon of Mesorhizobium loti Strain R7A and Its Symbiotic Activation by a Novel LacI/GalR-Family Regulator

“…Msi262 shows 71% identity to the R. etli iscN gene product that is thought to act as a scaffold protein for Fe-S biosynthesis. Mutants of R. etli defective in iscN showed a 90% reduction in nitrogen fixation [57]. Msi263 is a member of the IscU protein family (COG0822).…”