title: Regulation of the metC-cysK operon, involved in sulfur metabolism in Lactococcus lactis.
abstract: Sulfur metabolism in gram-positive bacteria is poorly characterized. Information on the molecular mechanisms of regulation of genes involved in sulfur metabolism is limited, and no regulator genes have been identified. Here we describe the regulation of the lactococcal metC-cysK operon, encoding a cystathionine beta-lyase (metC) and cysteine synthase (cysK). Its expression was shown to be negatively affected by high concentrations of cysteine, methionine, and glutathione in the culture medium, while sulfur limitation resulted in a high level of expression. Other sulfur sources tested showed no significant effect on metC-cysK gene expression. In addition we found that O-acetyl-l-serine, the substrate of cysteine synthase, was an inducer of the metC-cysK operon. Using a random mutagenesis approach, we identified two genes, cmbR and cmbT, involved in regulation of metC-cysK expression. The cmbT gene is predicted to encode a transport protein, but its precise role in regulation remains unclear. Disruption of cmbT resulted in a two- to threefold reduction of metC-cysK transcription. A 5.7-kb region containing the cmbR gene was cloned and sequenced. The encoded CmbR protein is homologous to the LysR family of regulator proteins and is an activator of the metC-cysK operon. In analogy to CysB from Escherichia coli, we propose that CmbR requires acetylserine to be able to bind the activation sites and subsequently activate transcription of the metC-cysK operon.
authors.affiliation: Wageningen Centre for Food Sciences, Wageningen, and Department of Flavour, Nutrition and Ingredients, NIZO Food Research, Ede, The Netherlands.
authors.forename: María
authors.initials: M
authors.lastname: Fernández
authors.forename: Michiel
authors.initials: M
authors.lastname: Kleerebezem
authors.forename: Oscar P
authors.initials: OP
authors.lastname: Kuipers
authors.forename: Roland J
authors.initials: RJ
authors.lastname: Siezen
authors.forename: Richard
authors.initials: R
authors.lastname: van Kranenburg
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D003547:Cysteine Synthase / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005809:Genes, Regulator; D013294:Lactococcus lactis / Q000235:genetics* / Q000378:metabolism; D008190:Lyases / Q000235:genetics*; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics*; D020161:Physical Chromosome Mapping; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C443981:CmbR protein, Lactococcus lactis; C443980:CmbT protein, Lactococcus lactis; D026901:Membrane Transport Proteins; D014157:Transcription Factors; D003547:Cysteine Synthase; D008190:Lyases; C019965:cystathionine beta-lyase