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 conditions; oxygen induction is lost when the hemA-lacZ fusion is expressed in strains of B. japonicum carrying mutations in fix 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 Bg/II 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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其它主题
Fixj protein; Escherichia coli proteins; Genetic regulation; Hemeproteins; Molecular sequence data; Lacz gene; 5-aminolevulinate synthase; Base sequence; Iron-sulfur proteins; Nucleic acid; Fixl protein; Nucleic acid; Sequence homology; Transcription (genetics); Dna-binding proteins; Bacterial; Aldehyde oxidoreductases; Species specificity; Hema promoter; Structural genes; Fixk protein; Deletions; Beta-galactosidase; Recombinant fusion proteins; Drug effects
语言
英语
类型
Journal Article; Text
2024-02-28
2026-02-03
MODS