Cloning of a Corynebacterium diphtheriae iron-repressible gene that shares sequence homology with the AhpC subunit of alkyl hydroperoxide reductase of Salmonella typhimurium.

To understand how Corynebacterium diphtheriae responds to iron limitation, we compared the sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) protein profiles of both wild-type cells and iron uptake mutants grown in either high- or low-iron medium. The removal of iron by ethylene diamine di-(o-hydroxy-phenyl acetic acid) from the growth medium of wild-type cells resulted in induction of at least 14 polypeptides. DirA, a major iron-repressible polypeptide, was purified from wild-type cells by preparative SDS-PAGE, and the dirA structural gene was isolated from a genomic library of nontoxigenic C. diphtheriae. The nucleotide sequence of dirA was determined, and the deduced amino acid sequence of DirA revealed strong homologies with the AhpC subunit of Salmonella typhimurium alkyl hydroperoxide reductase and polypeptides of other microorganisms associated with oxidation reduction activity. Like AhpC, cloned DirA reduced the susceptibility of an Escherichia coli ahp mutant to cumene hydroperoxide, suggesting that DirA has alkyl hydroperoxide reductase activity.