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J. Bacteriol. doi:10.1128/JB.01876-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

The IclR-type transcriptional repressor LtbR regulates the expression of leucine and tryptophan biosynthesis genes in the amino acid producer Corynebacterium glutamicum

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

^* To whom correspondence should be addressed. Email: Andreas.Tauch{at}Genetik.Uni-Bielefeld.DE.

	Abstract

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, when 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/_CATAGTG^A/_GGA 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 40mers 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.

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