Regulation of the expression level of transcription factor XylS reveals new functional insight into its induction mechanism at the Pm promoter.

Background: XylS is the positive regulator of the inducible Pm promoter, originating from Pseudomonas putida, where the system controls a biochemical pathway involved in degradation of aromatic hydrocarbons, which also act as inducers. The XylS/Pm positive regulator/promoter system is used for recombinant gene expression and the output from Pm is known to be sensitive to the intracellular XylS concentration.

Results: By constructing a synthetic operon consisting of xylS and luc, the gene encoding luciferase, relative XylS expression levels could be monitored indirectly at physiological concentrations.

Combinatorial engineering for heterologous gene expression.

Tools for strain engineering with predictable outcome are of crucial importance for the nascent field of synthetic biology. The success of combining different DNA biological parts is often restricted by poorly understood factors deriving from the complexity of the systems. We have previously identified variants for different regulatory elements of the expression cassette XylS/Pm.

Strong stimulation of recombinant protein production in Escherichia coli by combining stimulatory control elements in an expression cassette.

Background: The XylS/Pm expression system has been used to produce recombinant proteins at industrial levels in Escherichia coli. Activation of transcription from the Pm promoter takes place in the presence of benzoic acid or derivatives of it. Previous mutagenesis studies resulted in identification of several variants of the expression control elements xylS (X), Pm (P) and the 5'-untranslated region (U) that individually gave rise to strongly stimulated expression.

Electronic structure of solids with competing periodic potentials.

When electrons are subject to a potential with two incommensurate periods, translational invariance is lost, and no periodic band structure is expected. However, model calculations based on nearly free one-dimensional electrons and experimental results from high-resolution photoemission spectroscopy on a quasi-one-dimensional material do show dispersing band states with signatures of both periodicities. Apparent band structures are generated by the nonuniform distribution of electronic spectral weight over the complex eigenvalue spectrum.

Dynamical properties of the one-dimensional band insulator (NbSe4)3I.

Optical and photoemission experiments reveal unexpected spectral signatures of one-dimensional band insulators. In the model compound (NbSe (4))3I the optical conductivity decays as a power law sigma(1)(omega) approximately omega(-4.25) above a sharp gap edge.