STRUCTURES OF THE APO-ACTIVATED AND THE METAL ION-ACTIVATED FORMS OF THE DIPHTHERIA TOX REPRESSOR FROM CORYNEBACTERIUM-DIPHTHERIAE

The diphtheria fox repressor (DtxR) of Corynebacterium diphtheriae pla ys a critical role in the regulation of diphtheria toxin expression an d the control of other iron-sensitive genes, The crystal structures of apo-DtxR and of the metal ion-activated form of the repressor have be en solved and used to identify motifs involved in DNA and metal ion bi nding, Residues involved in binding of the activated repressor to the diphtheria fox operator, glutamine 43, arginine 47, and arginine 50, w ere located and confirmed by site-directed mutagenesis. Previous bioch emical and genetic data can be explained in terms of these structures. Conformational differences between apo- and Ni-DtxR are discussed wit h regard to the mechanism of action of this repressor.