The virulence genes of pathogenic enterobacteria are concentrated in genomic islands acquired by horizontal transfer during evolution. The expression of these genes outside the infection phase is detrimental to the bacterium and is therefore highly regulated. A major regulatory mechanism relies on the histone-like protein H-NS, which binds to AT-rich sites characteristic of horizontally acquired DNA and forms oligomeric structures that inhibit transcription over extended regions. These regions, however, remain exposed to invasive transcription from neighboring regions or to H-NS repression defects. Our data support a model in which the transcription elongation factor NusG “secures” the inhibition of virulence genes by stimulating the activity of the transcription termination factor Rho in regions silenced by H-NS. Remarkably, NusG changes the specificity of the Rho factor, which alone preferentially targets C-rich regions. The perturbation of this NusG/Rho-dependent mechanism in Salmonella has profound physiological consequences, probably because unstopped transcription in H-NS -targeted regions feeds a feed-forward activation cascade leading to the uncontrolled expression of pathogenicity islands and co-regulated loci.
"Cell signalling" group led by the Dr H. Bénédetti has published a video paper in JOVE, Journal of Visualized Experiments, a peer-reviewed scientific journal that publishes experimental methods in video format.
This paper belongs to the Method section focusing on basic technics in Biochemistry.
Different experiments are detailled:
- Transient cell transfections
- Protein extraction
- Study of protein/protein interaction by co-immunoprecipitation experiments
- Study of kinase activity by g32P-[ATP] labeling or by using phospho-specific antibodies
All these different technics are illustrated with data obtained by the group on LIMK2-1, a new protein the team has just pointed out and characterized. LIMK2-1 protein does exist, and it is very atypical in the way it regulates actin cytoskeleton remodeling.
The meteorites bring it regularly, but it has left no trace of it. It has been identified and analyzed by researchers from the CNRS, Chimie ParisTech, the Universities of Tours and Lille. Their publication, in the journal Geochimica and Cosmochimica Acta, offers a first model to distinguish these molecules from elsewhere from those produced on Earth.
References of the article:
D. Gourier et al.
Extraterrestrial organic matter preserved in 3.33 Ga sediments from Barberton, South Africa.
Geochimica and Cosmochimica Acta - May 2019 - DOI: 10.1016 / j.gca.2019.05.009
The article presents a new interpretation of neutron scattering spectra by molecular systems that has much in common with the Franck-Condon theory describing the vibrational transitions in a molecule after absorption or emission of a photon. The principal elements are the quantum probabilities for the transitions between the energy levels of the studied system, which are induced by diffusion of a neutron. In this case, the fundamental concept of "energy landscapes", which was introduced by Hans Frauenfelder to describe the internal dynamics of proteins in terms of "jumps" between the minima of their (free) internal energy, can be integrated in the analysis of neutron scattering spectra by complex systems in general. The theory also provides an intuitive physical interpretation of Van Hove's correlation functions in the quantum regime, as well as their classical limit, which is usually considered in the analysis of quasi-elastic spectra of neutrons from proteins and other complex molecular systems.
The success of this method relies on the use of nonvolatile liquid matrices, which avoids the passage through the solid phase conventionally used in MALDI and the denaturation of the non-covalent assemblies. By their increased viscosity, these matrices also have the advantage of better mimicking the cluttered environments of living organisms.
The reliability of this method has been shown for non-covalent protein protein and ligand protein systems. This new approach could be used for screening of therapeutic protein ligands and facilitating the analysis of membrane protein complexes by mass spectrometry.