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DNA topoisomerase I acts as supercoiling sensor for bacterial transcription elongation
No full textInternational audienceDuring transcription, RNA polymerase (RNAP) continuously unwinds and rewinds DNA, generating negative and positive supercoils upstream and downstream, respectively. Using single-particle cryo-EM, we elucidated how bacterial RNAP and DNA topoisomerase I (TopoI), which relaxes negative supercoils, operate in close spatial proximity. TopoI binds to relaxed DNA upstream of RNAP, and this involves a conformational switch in the TopoI functional domains. This suggests that TopoI exerts a sensing role before the formation of negative supercoils. On DNA substrates mimicking negatively supercoiled DNA, TopoI threads one strand into the active site for cleavage and binds the complementary strand with an auxiliary domain. Transcriptomic and phenotypic analyses suggest that mutations affecting conformational changes in TopoI impact gene expression and operon polarity in bacteria. In summary, we propose a comprehensive model for DNA relaxation in the proximity of active bacterial transcription
Metabolic profiling reveals first evidence of fumigating drug plant Peganum harmala in Iron Age Arabia
No full textInternational audienceThe utilization of medicinal and psychoactive plants in the past represents a pivotal intersection of culture, health, and biodiversity. While such plants in Arabia have been known from classical and medieval textual records, this study provides material evidence of the use of one such plant for fumigation already in the Iron Age. Through metabolic profiling of organic residues recovered from archaeological artefacts at the oasis of Qurayyah, Northwest Arabia, we identified the drug plant Peganum harmala . Renowned for its antibacterial, psychoactive and multiple therapeutic properties, its presence highlights the deliberate utilization of local pharmacopeia by ancient communities. This discovery represents not only the first evidence for its use in Iron Age Arabia, but also the most ancient, radiometrically dated material evidence of Peganum harmala being used for fumigation globally. Beyond their health benefits, these plants were also valued for their sensory and affective properties. Documenting, understanding and preserving these ancient knowledge systems enriches our understanding of ancient traditions while safeguarding the region’s intangible cultural heritage
La Maison franco-japonaise, un siècle d’échanges scientifiques et d’histoire intellectuelle
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« L’histoire de la démocratie, ce n’est pas seulement l’histoire du suffrage universel »
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Chimie moléculaire : nouveaux défis et innovation durable: leçon inaugurale prononcée au Collège de France le jeudi 7 mars 2024
No full textInternational audienceLa synthèse moléculaire est la science qui consiste à transformer des molécules de départ pour en créer de nouvelles plus élaborées. Physiquement, elle requiert de former de nouvelles liaisons entre des atomes grâce à un processus d'activation moléculaire qui peut être thermique, photochimique, mécanique ou reposer sur une catalyse. Après plus d’un siècle de développements industriels et de constante innovation, la nécessité d’une transition énergétique et d’une durabilité des ressources réoriente les recherches dans le domaine de la synthèse moléculaire, notamment des processus d’activation, afin de produire des molécules aux propriétés optimisées pour une population mondiale en augmentation
Kinematics of the lens host S0 galaxy NGC 1553 : role of secular processes
No full textInternational audienceWe investigated the central structure of the S0 galaxy NGC 1553, to understand its origin and the underlying dynamical processes that shape it. The high-resolution integral field spectroscopic data from the Multi Unit Spectroscopic Explorer (MUSE) reveal a well-ordered rotation pattern, consisting of a (i) rapidly rotating nuclear disc that is somewhat decoupled from the main disc, and (ii) an inner lens; we collectively refer to these structures as the 'disc-lens'. The central peak in the velocity dispersion indicates the presence of a classical bulge. The nuclear disc is dynamically colder than the surrounding disc, while the lens is dynamically hotter. The higher-order Gauss-Hermite moments, h 3 and h 4 , further characterise the stellar kinematics. An anti-correlation between the line-of-sight velocity and skewness (h 3 ) is consistent with regular rotation. In contrast, the ring-like increase in kurtosis (h 4 ) confirms the presence of the nuclear disc component. Unsharp masking of HST images has previously revealed a nuclear bar and faint spiral structures within the central ∼10 arcsec, supporting the role of secular evolution. The mass-weighted stellar age map reveals an old stellar population in the central regions, with a high metallicity that suggests the in situ formation of the disc-lens from disc material. We discuss possible formation scenarios for the disc-lens, including both minor mergers and secular processes, and examine the influence of the Dorado group environment on NGC 1553. Our findings suggest that the disc-lens in NGC 1553 formed during the early stages of the galaxy's evolution. However, its subsequent development has been shaped by internal and external processes. These results provide new insights into the origin and evolution of kinematically distinct substructures in S0 galaxies
Symmetries, conservation laws and entanglement in non-Hermitian fermionic lattices
No full textInternational audienceNon-Hermitian quantum many-body systems feature steady-state entanglement transitions driven by the competition between unitary dynamics and dissipation. In this work, we reveal the fundamental role of conservation laws in shaping this competition. Focusing on translation-invariant non-interacting fermionic models with U(1) symmetry, we present a theoretical framework to understand the structure of the steady-state of these models and their entanglement content based on two ingredients: the nature of the spectrum of the non-Hermitian Hamiltonian and the constraints imposed on the steady-state single-particle occupation by the conserved quantities. These emerge from an interplay between Hamiltonian symmetries and initial state, due to the non-linearity of measurement back-action. For models with complex energy spectrum, we show that the steady state is obtained by filling single-particle right eigenstates with the largest imaginary part of the eigenvalue. As a result, one can have partially filled or fully filled bands in the steady-state, leading to an entanglement entropy undergoing a filling-driven transition between critical sub-volume scaling and area-law, similar to ground-state problems. Conversely, when the spectrum is fully real, we provide evidence that local observables can be captured using a diagonal ensemble, and the entanglement entropy exhibits a volume-law scaling independently on the initial state, akin to unitary dynamics. We illustrate these principles in the Hatano-Nelson model with periodic boundary conditions and the non-Hermitian Su-Schrieffer-Heeger model, uncovering a rich interplay between the single-particle spectrum and conservation laws in determining the steady-state structure and the entanglement transitions. These conclusions are supported by exact analytical calculations and numerical calculations relying on the Faber polynomial method
Many-body open quantum systems
No full textInternational audienceThese lecture notes discuss the recent theoretical advances in the understanding of open quantum many-body physics in platforms where both dissipative and coherent processes can be tuned and controlled to a high degree. We start by reviewing the theoretical frameworks and methods used to describe and tackle open quantum many-body systems. We then discuss the use of dissipative processes to engineer many-body stationary states with desired properties and the emergence of dissipative phase transitions arising out of the competition between coherent evolution and dissipation. We review the dynamics of open quantum many body systems in the presence of correlated many-body dissipative processes, such as heating and many-body losses. Finally we provide a different perspective on open quantum many-body systems by looking at stochastic quantum trajectories, relevant for the case in which the environment represents a monitoring device, and the associated measurement-induced phase transitions
