Analysis of truncated variants of the iron dependent transcriptional regulators from Corynebacterium diphtheriae and Mycobacterium tuberculosis

Iron dependent regulatory proteins of the diphtheria toxin repressor family regulate transcription in a variety of bacterial species. These regulators have three domains. Domains 1 and 2 are required for DNA- and metal-binding while the role of the third domain is only partially defined. We compared full-length and carboxyl-terminally truncated variants of Corynebacterium diphtheriae DtxR and Mycobacterium tuberculosis IdeR for recognition by antibodies, DNA binding, and repressor activity. The third domain of DtxR contains immunodominant epitopes and is required for full repressor activity in an Escherichia coli reporter system, but it is not required for binding to DNA in vitro. In contrast, the third domain of IdeR is required both for full DNA binding activity in vitro and for repressor activity in vivo. DtxR and IdeR differ significantly in their requirements for domain 3 for DNA-binding and repressor activity.