ThrR, a DNA-binding transcription factor involved in controlling threonine biosynthesis in Bacillus subtilis.
The threonine dehydratase IlvA is part of the isoleucine biosynthesis pathway in the Gram-positive model bacterium Bacillus subtilis. Consequently, deletion of ilvA causes isoleucine auxotrophy. It has been reported that ilvA pseudo-revertants having a derepressed hom-thrCB operon appear in the presence of threonine. Here we have characterized two classes of ilvA pseudo-revertants. In the first class the hom-thrCB operon was derepressed unmasking the threonine dehydratase activity of the threonine synthase ThrC. In the second class of mutants, threonine biosynthesis was more broadly affected. The first class of ilvA pseudo-revertants had a mutation in the Phom promoter (P*hom ), resulting in constitutive expression of the hom-thrCB operon. In the second class of ilvA pseudo-revertants, the thrR gene encoding a putative DNA-binding protein was inactivated, also resulting in constitutive expression of the hom-thrCB operon. Here we demonstrate that ThrR is indeed a DNA-binding transcription factor that regulates the hom-thrCB operon and the thrD aspartokinase gene. DNA binding assays uncovered the DNA-binding site of ThrR and revealed that the repressor competes with the RNA polymerase for DNA binding. This study also revealed that ThrR orthologs are ubiquitous in genomes from the Gram-positive phylum Firmicutes and in some Gram-negative bacteria.
Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany.
Jonathan
J
Rosenberg
Department of Genetics, Bacterial Genetics, Friedrich Schiller University Jena, Jena, Germany.
Peter
P
Müller
Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany.
Sabine
S
Lentes
Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany.
Martin J
MJ
Thiele
Department of Microbiology, Ohio State University, Columbus, OH, 43210, USA.
Daniel R
DR
Zeigler
Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany.
Dominik
D
Tödter
Boston Biomedical Research Institute, Boston, MA, USA.
Henry
H
Paulus
Department of Genetics, Bacterial Genetics, Friedrich Schiller University Jena, Jena, Germany.
Sabine
S
Brantl
Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany.
Jörg
J
Stülke
Department of General Microbiology, Georg August University Göttingen, Grisebachstr. 8, Göttingen, 37077, Germany.
Fabian M
FM
Commichau
D001224:Aspartic Acid / Q000378:metabolism; D001412:Bacillus subtilis / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D019757:Carbon-Oxygen Lyases / Q000378:metabolism; D004247:DNA / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005798:Genes, Bacterial; D009154:Mutation; D009876:Operon; D011401:Promoter Regions, Genetic; D013912:Threonine / Q000096:biosynthesis* / Q000378:metabolism; D013913:Threonine Dehydratase / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics
D004268:DNA-Binding Proteins; D014157:Transcription Factors; D013912:Threonine; D001224:Aspartic Acid; D004247:DNA; D019757:Carbon-Oxygen Lyases; C023160:threonine synthase; D013913:Threonine Dehydratase