Discovery of a Novel Metalloregular Family: Structure/Function Studies of E. Coli Rcnr

The first row transition metal ions- Mn, Fe, Co, Ni, Cu and Zn are vital cofactors for proteins involved in diverse processes including photosynthesis, oxidative respiration and protein translation. Despite these essential functions, excess metal ions can lead to cell death through the generation of oxidative damage or the occupation of non-native metal sites. Acquiring metal ions from the environment while limiting possible toxic effects requires the coordinated regulation of metal uptake, trafficking and efflux, which in bacteria is often carried out by metal-responsive transcription factors: metalloregulators). Nickel homeostasis in E. coli is an ideal model system for understanding the relationships between metal physiology and metalloregulator function, as cellular nickel requirements are primarily limited to Ni-Fe hydrogenases, the levels of which can be easily controlled by different electron acceptors in the medium. While the previously studied Ni-responsive metalloregulator NikR controls Ni import, this thesis describes the identification of RcnR, a novel regulator of Ni efflux. RcnR is the founding member of the RcnR/CsoR family of metalloregulators that are found throughout the eubacterial kingdom and respond to a range of different environmental stresses including metal ions, aldehydes and oxidative stress. RcnR-dependent gene repression is directly relieved by excess intracellular Ni(II) or Co(II), which bind to the protein at similar high-spin, six-coordinate, distorted octahedral binding sites. The metal site is distinct from the four coordinate high-affinity site of NikR, and these differences lead to the sequential repression of nickel import and activation of nickel efflux with respect to increasing extracellular nickel levels. Unlike other transcription factors, RcnR/CsoR proteins contain a unique DNA binding motif that recognizes DNA sequences containing G-tracts flanked by AT-rich inverted repeats. RcnR binds to a pair of sites in the rcnA-rcnR intergenic region leading to DNA wrapping, and repression of both genes. The identification of this new metalloregulator family and subsequent investigation of the functional properties of one member, RcnR, provides a solid foundation for understanding the stress responses mediated by other members of this family and the mechanisms of DNA binding by the unique, all-helical fold

A progression of Methodist radicalism : an examination of the history and ethos of the first sixty years of the Nazarites and their heirs (1855-1915) in their social and religious context

https://place.asburyseminary.edu/ecommonsatsdissertations/2189/thumbnail.jp

A user-friendly fully digital TDPAC-spectrometer

A user-friendly fully digital TDPAC-spectrometer with six detectors and fast digitizers using Field Programmable Gate Arrays is described and performance data are given

Conformational and thermodynamic hallmarks of DNA operator site specificity in the copper sensitive operon repressor from Streptomyces lividans

Metal ion homeostasis in bacteria relies on metalloregulatory proteins to upregulate metal resistance genes and enable the organism to preclude metal toxicity. The copper sensitive operon repressor (CsoR) family is widely distributed in bacteria and controls the expression of copper efflux systems. CsoR operator sites consist of G-tract containing pseudopalindromes of which the mechanism of operator binding is poorly understood. Here, we use a structurally characterized CsoR from Streptomyces lividans (CsoRSl) together with three specific operator targets to reveal the salient features pertaining to the mechanism of DNA binding. We reveal that CsoRSl binds to its operator site through a 2-fold axis of symmetry centred on a conserved 5′-TAC/GTA-3′ inverted repeat. Operator recognition is stringently dependent not only on electropositive residues but also on a conserved polar glutamine residue. Thermodynamic and circular dichroic signatures of the CsoRSl-DNA interaction suggest selectivity towards the A-DNA-like topology of the G-tracts at the operator site. Such properties are enhanced on protein binding thus enabling the symmetrical binding of two CsoRSl tetramers. Finally, differential binding modes may exist in operator sites having more than one 5′-TAC/GTA-3′ inverted repeat with implications in vivo for a mechanism of modular control. © 2013 The Author(s)

Planning the Kitchen

Provides a brief discussion of new trends in kitchen planning

Household care and cleaning

This circular replaces Circular 416.Cover title.Includes index

Functional and expression analysis of the metal-inducible dmeRF system from Rhizobium legumionosarum bv. viciae

A gene encoding a homolog to the cation diffusion facilitator protein DmeF from Cupriavidus metallidurans has been identified in the genome of Rhizobium leguminosarum UPM791. The R. leguminosarum dmeF gene is located downstream of an open reading frame (designated dmeR) encoding a protein homologous to the nickel- and cobalt-responsive transcriptional regulator RcnR from Escherichia coli. Analysis of gene expression showed that the R. leguminosarum dmeRF genes are organized as a transcriptional unit whose expression is strongly induced by nickel and cobalt ions, likely by alleviating the repressor activity of DmeR on dmeRF transcription. An R. leguminosarum dmeRF mutant strain displayed increased sensitivity to Co(II) and Ni(II), whereas no alterations of its resistance to Cd(II), Cu(II), or Zn(II) were observed. A decrease of symbiotic performance was observed when pea plants inoculated with an R. leguminosarum dmeRF deletion mutant strain were grown in the presence of high concentrations of nickel and cobalt. The same mutant induced significantly lower activity levels of NiFe hydrogenase in microaerobic cultures. These results indicate that the R. leguminosarum DmeRF system is a metal-responsive efflux mechanism acting as a key element for metal homeostasis in R. leguminosarum under free-living and symbiotic conditions. The presence of similar dmeRF gene clusters in other Rhizobiaceae suggests that the dmeRF system is a conserved mechanism for metal tolerance in legume endosymbiotic bacteria