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The IclR-Type Transcriptional Repressor LtbR Regulates the Expression of Leucine and Tryptophan Biosynthesis Genes in the Amino Acid Producer Corynebacterium glutamicum

Iris Brune,^1,2 Nina Jochmann,^1,2 Karina Brinkrolf,^1,3 Andrea T. Hüser,¹ Robert Gerstmeir,^4, Bernhard J. Eikmanns,⁴ Jörn Kalinowski,¹ Alfred Pühler,² and Andreas Tauch^1*

Institut für Genomforschung, Centrum für Biotechnologie, Universität Bielefeld, Universitätsstraße 25, D-33615 Bielefeld, Germany,¹ Lehrstuhl für Genetik, Fakultät für Biologie, Universität Bielefeld, Universitätsstraße 25, D-33615 Bielefeld, Germany,² International NRW Graduate School in Bioinformatics and Genome Research, Centrum für Biotechnologie, Universität Bielefeld, Universitätsstraße 25, D-33615 Bielefeld, Germany,³ Institute of Microbiology and Biotechnology, University of Ulm, D-89069 Ulm, Germany⁴

Received 13 December 2006/ Accepted 19 January 2007

The transcriptional regulator Cg1486 of Corynebacterium glutamicum ATCC 13032 is a member of the IclR protein family and belongs to the conserved set of regulatory proteins in corynebacteria. A defined deletion in the cg1486 gene, now designated ltbR (leucine and tryptophan biosynthesis regulator), led to the mutant strain C. glutamicum IB1486. According to whole-genome expression analysis by DNA microarray hybridizations, transcription of the leuB and leuCD genes encoding enzymes of the leucine biosynthesis pathway was enhanced in C. glutamicum IB1486 compared with the wild-type strain. Moreover, the genes of the trpEGDCFBA operon involved in tryptophan biosynthesis of C. glutamicum showed an enhanced expression in the cg1486 mutant strain. Bioinformatics pattern searches in the upstream regions of the differentially expressed genes revealed the common 12-bp motif CA(T/C)ATAGTG(A/G)GA that is located downstream of the –10 region of the mapped promoter sequences. DNA band shift assays with a streptavidin-tagged LtbR protein demonstrated the specific binding of the purified protein to 40-mers containing the 12-bp motif localized in front of leuB, leuC, and trpE, thereby confirming the direct regulatory role of LtbR in the expression of the leucine and tryptophan biosynthesis pathway genes of C. glutamicum. Genes homologous with ltbR were detected upstream of the leuCD genes in almost all sequenced genomes of bacteria belonging to the taxonomic class Actinobacteria. The ltbR-like genes of Corynebacterium diphtheriae, Corynebacterium jeikeium, Mycobacterium bovis, and Bifidobacterium longum were cloned and shown to complement the deregulation of leuB, leuCD, and trpE gene expression in C. glutamicum IB1486.

Published ahead of print on 26 January 2007.

Present address: Degussa AG, Project House ProFerm, D-33790 Halle/Westfalen, Germany.

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