Gh. Wu et al., THE CYDR GENE-PRODUCT, REQUIRED FOR REGULATION OF CYTOCHROME BD EXPRESSION IN THE OBLIGATE AEROBE AZOTOBACTER-VINELANDII, IS AN FNR-LIKE PROTEIN, Microbiology, 143, 1997, pp. 2197-2207
The cytochrome bd complex in the obligately aerobic diazotroph Azotoba
cter vinelandii is an oxidase, which, in vivo, has a low affinity for
oxygen and is required for respiratory protection of nitrogenase. Muta
tions caused by insertion of Tn5-B20 upstream of the structural genes
(cydAB) for cytochrome bd result in over-expression of this oxidase an
d, for unexplained reasons, inability of the organism to grow microaer
obically. Cloning and sequencing of this upstream region revealed a ge
ne, 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 cyd
AB expression. Refined mapping data for three insertions in cydR are p
resented. The cloned cydR gene complemented anaerobic growth of Escher
ichia coil fnr mutants and strongly enhanced expression of a narG-lacZ
fusion in an E. coil fnr mutant.