Oxygen control of the Bradyrhizobium japonicum hemA gene.
The hemA gene of Bradyrhizobium japonicum, which encodes the first enzyme in the heme biosynthetic pathway, is regulated by oxygen. Up to ninefold induction of beta-galactosidase activity is seen when cultures of B. japonicum containing either a plasmid-encoded or a chromosomally integrated hemA-lacZ fusion are shifted to restricted aeration. The oxygen effect is mediated via the FixLJ two-component regulatory system, which regulates the expression of a number of genes involved in the nitrogen fixation process in response to low-oxygen conductions; oxygen induction is lost when the hemA-lacZ fusion is expressed in strains of B. japonicum carrying mutations in fixL or fixJ. The B. japonicum hemA promoter region contains a sequence identical to the Escherichia coli Fnr binding site (positions -46 to -33 relative to the hemA transcription start site). Fnr is a regulatory protein necessary for the oxygen-regulated expression of anaerobic respiratory genes. Activity of a hemA-lacZ fusion construct in which the Fnr box-like sequence was replaced with a BglII site is not induced in B. japonicum cultures grown under restricted aeration. The fnr homolog fixK is FixLJ dependent. Collectively, these data suggest a role for the rhizobial Fnr-like protein, FixK, in the regulation of hemA. Furthermore, the coregulation of hemA with symbiotically important genes via FixLJ is consistent with the idea that hemA is required in the nodule as well as under free-living conditions.
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K M
KM
Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
Guerinot
M L
ML
D000445:Aldehyde Oxidoreductases / Q000096:biosynthesis* / Q000235:genetics; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D006420:Hemeproteins / Q000378:metabolism; D000071677:Histidine Kinase; D007506:Iron-Sulfur Proteins; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics; D010100:Oxygen / Q000494:pharmacology*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012230:Rhizobiaceae / Q000187:drug effects / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D013559:Symbiosis / Q000235:genetics
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C060704:FNR protein, E coli; D006420:Hemeproteins; D007506:Iron-Sulfur Proteins; D011993:Recombinant Fusion Proteins; C069289:FixJ protein, Bacteria; D000445:Aldehyde Oxidoreductases; C067282:glutamyl tRNA reductase; C067929:FixL protein, Bacteria; D000071677:Histidine Kinase; D010100:Oxygen