title: Analysis of a taurine-dependent promoter in Sinorhizobium meliloti that offers tight modulation of gene expression.
abstract: BACKGROUND
  Genetic models have been developed in divergent branches of the class Alphaproteobacteria to help answer a wide spectrum of questions regarding bacterial physiology. For example, Sinorhizobium meliloti serves as a useful representative for investigating rhizobia-plant symbiosis and nitrogen fixation, Caulobacter crescentus for studying cell cycle regulation and organelle biogenesis, and Zymomonas mobilis for assessing the potentials of metabolic engineering and biofuel production. A tightly regulated promoter that enables titratable expression of a cloned gene in these different models is highly desirable, as it can facilitate observation of phenotypes that would otherwise be obfuscated by leaky expression.
  
  
  RESULTS
  We compared the functionality of four promoter regions in S. meliloti (P(araA), P(tauA), P(rhaR), and P(melA)) by constructing strains carrying fusions to the uidA reporter in their genomes and measuring beta-glucuronidase activities when they were induced by arabinose, taurine, rhamnose, or melibiose. P(tauA) was chosen for further study because it, and, to a lesser extent, P(melA), exhibited characteristics suitable for efficient modulation of gene expression. The levels of expression from P(tauA) depended on the concentrations of taurine, in both complex and defined media, in S. meliloti as well as C. crescentus and Z. mobilis. Moreover, our analysis indicated that TauR, TauC, and TauY are each necessary for taurine catabolism and substantiated their designated roles as a transcriptional activator, the permease component of an ABC transporter, and a major subunit of the taurine dehydrogenase, respectively. Finally, we demonstrated that P(tauA) can be used to deplete essential cellular factors in S. meliloti, such as the PleC histidine kinase and TatB, a component of the twin-arginine transport machinery.
  
  
  CONCLUSIONS
  The P(tauA) promoter of S. meliloti can control gene expression with a relatively inexpensive and permeable inducer, taurine, in diverse alpha-proteobacteria. Regulated expression of the same gene in different hosts can be achieved by placing both tauR and P(tauA) on appropriate vectors, thus facilitating inspection of conservation of gene function across species.
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. minamostafavi@yahoo.com.
authors.forename: Mina
authors.initials: M
authors.lastname: Mostafavi
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. jaineelewis@hotmail.com.
authors.forename: Jainee Christa
authors.initials: JC
authors.lastname: Lewis
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. tsaini@mail.sfsu.edu.
authors.forename: Tanisha
authors.initials: T
authors.lastname: Saini
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. ianios1@mail.sfsu.edu.
authors.forename: Julian Albert
authors.initials: JA
authors.lastname: Bustamante
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. igao614@gmail.com.
authors.forename: Ivan Thomas
authors.initials: IT
authors.lastname: Gao
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. tuyettran53@hotmail.com.
authors.forename: Tuyet Thi
authors.initials: TT
authors.lastname: Tran
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. sking@mail.sfsu.edu.
authors.forename: Sean Nicholas
authors.initials: SN
authors.lastname: King
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. huangzz@sfsu.edu.
authors.forename: Zhenzhong
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA. chenj@sfsu.edu.
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Chen
mesh_terms: D019677:Artificial Gene Fusion; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D017930:Genes, Reporter; D005827:Genetics, Microbial / Q000379:methods; D005966:Glucuronidase / Q000032:analysis / Q000235:genetics; D008967:Molecular Biology / Q000379:methods; D011401:Promoter Regions, Genetic / Q000187:drug effects*; D016962:Sinorhizobium meliloti / Q000235:genetics*; D013654:Taurine / Q000378:metabolism*
chemical_list: D013654:Taurine; D005966:Glucuronidase