Transcriptional regulation of histidine biosynthesis genes in Corynebacterium glutamicum

Corynebacterium glutamicum, a gram-positive bacterium, has been widely used for industrial amino acid production. Corynebacterium glutamicum his genes are located and transcribed in two unlinked loci, hisEG and hisDCB-orf1-orf2-hisHA-impA-hisFI. The latter his operon starts the transcription at the C residue localized 196 bp upstream of the hisD ATG start codon. Our computer-based sequence analysis showed that the region corresponding to the untranslated 5' end of the transcript, named the hisD leader region, displays the typical features of the T-box transcriptional attenuation mechanism. Therefore, expression of the cat reporter gene under the control of the wild-type or mutated hisD leader regions was tested in multi-copy (pProm and pTer series) and in single-copy (pInt series) systems under conditions of sufficient or limited histidine. Our mutational studies led to the conclusion that the CAU histidine specifier and 5'-UGGA-3' sequence in the hisD leader region are required for the hisDCB-orf1-orf2-hisHA-impA-hisFI gene regulation. The cat gene expression from the wild-type leader region was negatively regulated by histidine. However, the cat gene expression from mutated leader regions was irresponsive to the level of histidine in the growth medium. Taken together, we propose that a T-box mediated attenuation mechanism is responsible for the gene expression of the hisDCB-orf1-orf2-hisHA-impA-hisFI operon in C. glutamicum.