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Transcriptional regulation of histidine biosynthesis genes in Corynebacterium glutamicum

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Abstract:

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.

Corynebacterium glutamicum, une bactérie positive à gram, a été largement utilisée dans la production industrielle d’acides aminés. Le gène his de C. glutamicum est localisé et transcrit dans deux loci non liés, hisEG et hisDBC-orf1-orf2-hisHA-impA-hisFI. Ce dernier opéron commence la transcription à un résidu C localisé 196 pb en amont de l’ATG de départ de hisD. Notre analyse de séquence sur ordinateur a montré que la région correspondant à l’extrémité 5′ du transcrit, appelée région leader de hisD, présente les caractéristiques typiques d’une boîte T responsable d’un mécanisme d’atténuation de la transcription. Ainsi, l’expression d’un gène rapporteur cat placé sous le contrôle de régions leader de hisD sauvage ou mutées a été testée dans des systèmes à copies multiples (séries pProm et pTer) ou à copie unique (série pInt) sous des conditions de disponibilité suffisante ou limitée en histidine. Nos études de mutagenèse ont permis de conclure que le codon CAU de l’histidine et la séquence 5′-AGGA-3′ de la région du leader de hisD sont requises à la régulation du gène hisDBC-orf1-orf2-hisHA-impA-hisFI. L’expression du gène cat placé sous le contrôle de la région leader sauvage est régulée négativement par l’histidine. Cependant, l’expression du gène cat contrôlée par les régions leader mutées n’était pas régulée par le niveau d’histidine du milieu de croissance. À partir de tous ces résultats, nous proposons qu’un mécanisme d’atténuation dépendante d’une boîte T est responsable de l’expression de l’opéron hisDBC-orf1-orf2-hisHA-impA-hisFI chez C. glutamicum.

Document Type: Research Article

Publication date: 2010-02-02

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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