The cydR gene product, required for regulation of cytochrome bd expression in the obligate aerobe Azotobacter vinelandii, is an Fnr-like protein

Microbiology (Reading). 1997 Jul;143 ( Pt 7):2197-207. doi: 10.1099/00221287-143-7-2197.


The cytochrome bd complex in the obligately aerobic diazotroph Azotobacter vinelandii is an oxidase, which, in vivo, has a low affinity for oxygen and is required for respiratory protection of nitrogenase. Mutations caused by insertion of Tn5-B20 upstream of the structural genes (cydAB) for cytochrome bd result in over-expression of this oxidase and, for unexplained reasons, inability of the organism to grow microaerobically. Cloning and sequencing of this upstream region revealed a gene, cydR. The deduced amino acid sequence of CydR indicates that it is a new member of the Fnr Class of regulators and that it represses cydAB expression. Refined mapping data for three insertions in cydR are presented. The cloned cydR gene complemented anaerobic growth of Escherichia coli fnr mutants and strongly enhanced expression of a narG-lacZ fusion in an E. coli fnr mutant.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Anaerobiosis
  • Azotobacter vinelandii / genetics*
  • Azotobacter vinelandii / metabolism
  • Bacterial Proteins / genetics*
  • Bacterial Proteins / metabolism
  • Base Sequence
  • Cloning, Molecular
  • Cytochrome b Group
  • Cytochromes / genetics*
  • Cytochromes / metabolism
  • Electron Transport Chain Complex Proteins*
  • Escherichia coli / genetics
  • Escherichia coli / growth & development
  • Escherichia coli Proteins*
  • Gene Expression Regulation, Bacterial*
  • Genes, Bacterial*
  • Genes, Regulator*
  • Iron-Sulfur Proteins / genetics*
  • Molecular Sequence Data
  • Oxidoreductases / genetics*
  • Oxidoreductases / metabolism
  • Repressor Proteins / genetics*


  • Bacterial Proteins
  • CydR protein, Azotobacter vinelandii
  • Cytochrome b Group
  • Cytochromes
  • Electron Transport Chain Complex Proteins
  • Escherichia coli Proteins
  • FNR protein, E coli
  • Iron-Sulfur Proteins
  • Repressor Proteins
  • Oxidoreductases
  • cytochrome bd terminal oxidase complex, E coli

Associated data

  • GENBANK/L43595