ArnR, a novel transcriptional regulator, represses expression of the narKGHJI operon in Corynebacterium glutamicum.
The narKGHJI operon that comprises putative nitrate/nitrite transporter (narK) and nitrate reductase (narGHJI) genes is required for the anaerobic growth of Corynebacterium glutamicum with nitrate as a terminal electron acceptor. In this study, we identified a gene, arnR, which encodes a transcriptional regulator that represses the expression of the narKGHJI operon in C. glutamicum cells under aerobic conditions. Disruption of arnR induced nitrate reductase activities of C. glutamicum cells and increased narKGHJI mRNA levels under aerobic growth conditions. DNA microarray analyses revealed that besides the narKGHJI operon, the hmp gene, which encodes flavohemoglobin, is negatively regulated by ArnR under aerobic conditions. Promoter-reporter assays indicated that arnR gene expression was positively autoregulated by its gene product, ArnR, under both aerobic and anaerobic conditions. Electrophoretic mobility shift assay experiments showed that purified hexahistidyl-tagged ArnR protein specifically binds to promoter regions of the narKGHJI operon and the hmp and arnR genes. A consensus sequence, TA(A/T)TTAA(A/T)TA, found in the promoter regions of these genes was demonstrated to be involved in the binding of ArnR. Effects on LacZ activity by deletion of the ArnR binding sites within the promoter regions fused to the reporter gene were consistent with the view that the expression of the narKGHJI operon is repressed by the ArnR protein under aerobic conditions, whereas the expression of the arnR gene is autoinduced by ArnR.
Nishimura
Taku
T
Research Institute of Innovative Technology for the Earth, 9-2 Kizugawadai, Kizugawa, Kyoto 619-0292, Japan.
Teramoto
Haruhiko
H
Vertès
Alain A
AA
Inui
Masayuki
M
Yukawa
Hideaki
H
D000332:Aerobiosis / Q000235:genetics; D027321:Anion Transport Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D016384:Consensus Sequence; D048230:Corynebacterium glutamicum / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D025461:Feedback, Physiological / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D006420:Hemeproteins / Q000235:genetics; D007506:Iron-Sulfur Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D050901:Nitrate Reductase / Q000235:genetics*; D000091285:Nitrate Transporters; D009876:Operon / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000235:genetics
D027321:Anion Transport Proteins; D001426:Bacterial Proteins; D006420:Hemeproteins; D007506:Iron-Sulfur Proteins; D000091285:Nitrate Transporters; D012097:Repressor Proteins; C086193:flavohemoprotein, Bacteria; D050901:Nitrate Reductase; D001616:beta-Galactosidase