， a Gram-positive， aerobic bacterium， is the causative agent of diphtheria and cutaneous infections. While mechanisms required for heme iron acquisition are well known in ， systems involved in the acquisition of other metals such as zinc and manganese remain poorly characterized. In this study， we identified a genetic region that encodes an ABC-type transporter () and that is flanked by two genes ( and ) encoding putative substrate binding proteins of the cluster 9 family， a related group of transporters associated primarily with the import of Mn and Zn. We showed that IutA and IutE are both membrane proteins with comparable Mn and Zn binding abilities. We demonstrated that the genes are cotranscri... More
， a Gram-positive， aerobic bacterium， is the causative agent of diphtheria and cutaneous infections. While mechanisms required for heme iron acquisition are well known in ， systems involved in the acquisition of other metals such as zinc and manganese remain poorly characterized. In this study， we identified a genetic region that encodes an ABC-type transporter () and that is flanked by two genes ( and ) encoding putative substrate binding proteins of the cluster 9 family， a related group of transporters associated primarily with the import of Mn and Zn. We showed that IutA and IutE are both membrane proteins with comparable Mn and Zn binding abilities. We demonstrated that the genes are cotranscribed and repressed in response to iron by the iron-responsive repressor DtxR. Transcription of was positively regulated in response to iron availability in a DtxR-dependent manner and was repressed in response to Zn by the Zn-dependent repressor Zur. Electrophoretic mobility shift assays showed that DtxR does not bind to the upstream region， which indicates that DtxR regulation of is indirect and that other regulatory factors controlled by DtxR are likely responsible for the iron-responsive regulation. Analysis of the promoter region identified a 50-bp sequence at the 3' end of the gene that is required for the DtxR-dependent and iron-responsive activation of the gene. These findings indicate that transcription of is controlled by a complex mechanism that involves multiple regulatory factors whose activity is impacted by both Zn and Fe. Vaccination against diphtheria prevents toxin-related symptoms but does not inhibit bacterial colonization of the human host by the bacterium. Thus， remains an important human pathogen that poses a significant health risk to unvaccinated individuals. The ability to acquire iron， zinc， and manganese is critical to the pathogenesis of many disease-causing organisms. Here， we describe a gene cluster in that encodes a metal importer that is homologous to broadly distributed metal transport systems， some with important roles in virulence in other bacterial pathogens. Two metal binding components of the gene cluster encode surface exposed proteins， and studies of such proteins may guide the development of second-generation vaccines for .
