NdgR, a common transcriptional activator for methionine and leucine biosynthesis in Streptomyces coelicolor.
We show here that NdgR, a known transcriptional activator of isopropylmalate dehydratase in actinomycetes, may have other targets in the cell. An in-frame deletion mutant of ndgR showed unexpectedly poor growth in defined minimal medium even in the presence of leucine. To our surprise, it was supplementation of cysteine and methionine that corrected the growth. Based on this, we propose that NdgR induces cysteine-methionine biosynthesis. Direct involvement of NdgR in the very last steps of methionine synthesis with methionine synthase (metH) and 5,10-methylenetetrahydrofolate reductase (metF) was examined. From a pulldown assay, it was seen that NdgR was enriched from crude cell lysates with a strong affinity to metH and metF upstream sequences. Direct physical interaction of NdgR with these targets was further examined with a gel mobility shift assay. ndgR, leuC, metH, and metF were inducible in M145 cells upon nutrient downshift from rich to minimal medium but were not induced in the ndgR knockout mutant. Taking these observations together, NdgR-dependent metH-metF expression would account for the abnormal growth phenotype of the ndgR mutant although there may be additional NdgR-dependent genes in the Cys-Met metabolic pathways. As the first transcriptional factor reported for regulating Cys-Met metabolism in Streptomyces, NdgR links two disparate amino acid families, branched-chain amino acids (BCAAs) and sulfur amino acids, at the transcriptional level. Considering that Cys-Met metabolism is connected to mycothiol and one-carbon metabolism, NdgR may have broad physiological impacts.
Institute of Molecular Biology and Genetics, Seoul National University, Seoul, South Korea.
Songhee H
SH
Kim
Bo-Rahm
BR
Lee
Ji-Nu
JN
Kim
Byung-Gee
BG
Kim
D045103:5,10-Methylenetetrahydrofolate Reductase (FADH2) / Q000378:metabolism; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000378:metabolism; D003545:Cysteine / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D007535:Isomerases / Q000235:genetics / Q000378:metabolism; D007930:Leucine / Q000096:biosynthesis*; D008715:Methionine / Q000096:biosynthesis*; D048372:Streptomyces coelicolor / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D014157:Transcription Factors; D008715:Methionine; D045103:5,10-Methylenetetrahydrofolate Reductase (FADH2); D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; C032241:isopropylmalate isomerase; D007535:Isomerases; D007930:Leucine; D003545:Cysteine