Topoisomerases promote replication fork pausing at proteinaceous barriers

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Living organisms have to faithfully duplicate all the DNA in their chromosomes once and only once during every cell division. Replication forks pause/slow/arrest/stall during progression through chromosomes at certain tight DNA/protein complexes known as Replication Fork Barriers (RFB).  This pausing is promoted by the Fork Pausing Complex (FPC, composed of the Tof1 and Csm3 proteins in budding yeast) and opposed by Rrm3 helicase, a motor-like protein believed to displace obstacles.

Maksym Shyian and collaborators in the Shore laboratory have now discovered that the Tof1-Csm3 complex promotes fork pausing independently of Rrm3 helicase, in contrast to an old model. Instead the Fork Pausing Complex was found to mediate topoisomerase I (Top1) association with the replisome, which, together with Top2, is essential for fork slowdown (replisome sTOP mechanism).

The study was published in Genes & Development on December 5, 2019.

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Plant phosphate homeostasis is regulated by an inositol pyrophosphate signaling molecule

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Phosphorus is an essential building block for nucleic acids and membranes, forms an important energy currency of the cell and can act as a signaling molecule. Soil-living organisms take up phosphorus in the form of inorganic phosphate. How cells ‘measure’ phosphate concentrations to maintain sufficient phosphate levels in their cells and tissues is poorly understood. The group of Michael Hothorn has now elucidated that phosphate homeostasis in plants is regulated by an inositol pyrophosphate signaling molecule, which is generated by a bifunctional kinase/phosphatase enzyme in response to changing ATP and phosphate levels. The signaling molecule then binds to a cellular receptor, which in turn inactivates a transcription factor regulating phosphate starvation responses. Thus, a signaling molecule relays the nutrient status of the plant to a signaling cascade, allowing for nutrient uptake, storage and redistribution. The groups of Dorothea Fiedler (Leibniz Institute for Molecular Pharmacology, Berlin, Germany), Alisdair Fernie (Max Planck Institute for Molecular Plant Physiology, Golm, Germany) and Gabriel Schaaf (University of Bonn, Germany) contributed to this study that was published in eLife on August 22.

Pushing and pulling nucleosomes to control transcription initiation

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Chromatin remodelers are protein machines that move or eject nucleosomes from the chromatin template to regulate gene expression. Kubik et al. show how two distinct classes of remodelers, which they call « pushers » and « pullers », interact genome-wide at promoter regions to determine both the frequency of gene transcription and the precise site of initiation.

A common regulatory mechanism for plant photoreceptor signaling

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Plants perceive light as an important environmental cue. They sense the UV-B part of the solar spectrum through the UVR8 photoreceptor that activates acclimatory responses associated with protection against this potentially damaging radiation. UVR8 enhances the stability of the HY5 transcription factor by inhibiting the activity of COP1, an E3 ubiquitin ligase that targets HY5 for degradation. The teams of Michael Hothorn and of Roman Ulm have now discovered that the UVR8 mechanism of action involves direct competition between active UVR8 and HY5 through interaction domain mimicry and overlapping binding sites on COP1. This mechanism was found to be conserved in other photoreceptor signaling pathways. The study was published in The EMBO Journal on July 15, 2019.

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Michel Milinkovitch and Robbie Loewith receive an ERC Advanced Grant

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After receiving an ERC Starting Grant in 2008 and an ERC Consolidator Grant in 2014, Robbie Loewith has been awarded an ERC Advanced Grant for his research project entitled “Tension of ENDOmembranes maintained by TORC1 (TENDO)”. The aim is to understand how TORC1 regulates, and is regulated by, vacuolar membrane tension.

The grant is endowed with 2.25 million Euros over 5 years.

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An ERC Advanced Grant has been awarded to Michel Milinkovitch for his research project entitled « Identifying how Evolution exploits physical properties of tissues to generate the complexity and diversity of Life (EVOMORPHYS)”. The aim is to identify the drivers of Life’s morphological complexity and diversity.

The grant is endowed with 2.5 million Euros over 5 years.

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Les graines héritent des souvenirs de leur mère

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Le groupe de Luis Lopez-Molina démontre que le contrôle maternel et environnemental de la dormance des graines s’effectue via des mécanismes épigénétiques inédits d’interférence par ARN. Publiée le 26 mars 2019 dans eLife, l’étude révèle que l’empreinte maternelle et celle des températures présentes lors du développement des graines sont transmises par des processus similaires.

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La savante organisation des plumes des oiseaux

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Une étude à laquelle ont collaboré Athanasia Tzika et Michel Milinkovitch démontre comment des signaux génétiques et mécaniques se combinent pour permettre la formation d’un réseau organisé de plumes chez les oiseaux, leur permettant de voler. Les résultats ont été publiés le 21 février 2019 dans PLOS Biology.

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Vidéo : formation des plumes chez un embryon de poulet

An operon-like transcript has been identified in plants

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Operons were thought to be absent in plants. The group of Michael Hothorn now reports the identification of an operon-like transcript in plants that allows for the concerted expression of a previously unknown cell-cycle regulator and a metabolic enzyme. This highly unusual transcript is conserved across the entire plant kingdom and is required for plant embryo development and growth. This study was published on February 8, 2019 in Nature Plants.

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