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Target site selection in CAST systems

Gio, 12/08/2021 - 18:43

Tough recyclable polyacetals

Gio, 12/08/2021 - 18:43

The timing of land plant origins

Gio, 12/08/2021 - 18:43

Gut bugs and systemic disease risk

Gio, 12/08/2021 - 18:43

Boridene: a 2D boride

Gio, 12/08/2021 - 18:43

A virtual memory T cell spectrum

Gio, 12/08/2021 - 18:43

Castration delays aging

Gio, 12/08/2021 - 18:43

Brakes off cyclin drives memory

Gio, 12/08/2021 - 18:43

Where can we find the fertilizer?

Gio, 12/08/2021 - 18:43

Tackling the Hubbard model

Gio, 12/08/2021 - 18:43

Watching grain boundaries

Gio, 12/08/2021 - 18:43

Nitrogen discourages legumes

Gio, 12/08/2021 - 18:43

Some light on diazotrophs

Gio, 12/08/2021 - 18:43

Molecular phenotyping reveals the identity of Barretts esophagus and its malignant transition

Gio, 12/08/2021 - 18:43

The origin of human metaplastic states and their propensity for cancer is poorly understood. Barrett’s esophagus is a common metaplastic condition that increases the risk for esophageal adenocarcinoma, and its cellular origin is enigmatic. To address this, we harvested tissues spanning the gastroesophageal junction from healthy and diseased donors, including isolation of esophageal submucosal glands. A combination of single-cell transcriptomic profiling, in silico lineage tracing from methylation, open chromatin and somatic mutation analyses, and functional studies in organoid models showed that Barrett’s esophagus originates from gastric cardia through c-MYC and HNF4A-driven transcriptional programs. Furthermore, our data indicate that esophageal adenocarcinoma likely arises from undifferentiated Barrett’s esophagus cell types even in the absence of a pathologically identifiable metaplastic precursor, illuminating early detection strategies.

Structural basis for target site selection in RNA-guided DNA transposition systems

Gio, 12/08/2021 - 18:43

CRISPR-associated transposition systems allow guide RNA–directed integration of a single DNA cargo in one orientation at a fixed distance from a programmable target sequence. We used cryo–electron microscopy (cryo-EM) to define the mechanism that underlies this process by characterizing the transposition regulator, TnsC, from a type V-K CRISPR-transposase system. In this scenario, polymerization of adenosine triphosphate–bound TnsC helical filaments could explain how polarity information is passed to the transposase. TniQ caps the TnsC filament, representing a universal mechanism for target information transfer in Tn7/Tn7-like elements. Transposase-driven disassembly establishes delivery of the element only to unused protospacers. Finally, TnsC transitions to define the fixed point of insertion, as revealed by structures with the transition state mimic ADP•AlF3. These mechanistic findings provide the underpinnings for engineering CRISPR-associated transposition systems for research and therapeutic applications.

Secreted pectin monooxygenases drive plant infection by pathogenic oomycetes

Gio, 12/08/2021 - 18:43

The oomycete Phytophthora infestans is a damaging crop pathogen and a model organism to study plant-pathogen interactions. We report the discovery of a family of copper-dependent lytic polysaccharide monooxygenases (LPMOs) in plant pathogenic oomycetes and its role in plant infection by P. infestans. We show that LPMO-encoding genes are up-regulated early during infection and that the secreted enzymes oxidatively cleave the backbone of pectin, a charged polysaccharide in the plant cell wall. The crystal structure of the most abundant of these LPMOs sheds light on its ability to recognize and degrade pectin, and silencing the encoding gene in P. infestans inhibits infection of potato, indicating a role in host penetration. The identification of LPMOs as virulence factors in pathogenic oomycetes opens up opportunities in crop protection and food security.

Observation of microwave shielding of ultracold molecules

Gio, 12/08/2021 - 18:43

Harnessing the potential wide-ranging quantum science applications of molecules will require control of their interactions. Here, we used microwave radiation to directly engineer and tune the interaction potentials between ultracold calcium monofluoride (CaF) molecules. By merging two optical tweezers, each containing a single molecule, we probed collisions in three dimensions. The correct combination of microwave frequency and power created an effective repulsive shield, which suppressed the inelastic loss rate by a factor of six, in agreement with theoretical calculations. The demonstrated microwave shielding shows a general route to the creation of long-lived, dense samples of ultracold polar molecules and evaporative cooling.

Chemically recyclable thermoplastics from reversible-deactivation polymerization of cyclic acetals

Gio, 12/08/2021 - 18:43

Identifying plastics capable of chemical recycling to monomer (CRM) is the foremost challenge in creating a sustainable circular plastic economy. Polyacetals are promising candidates for CRM but lack useful tensile strengths owing to the low molecular weights produced using current uncontrolled cationic ring-opening polymerization (CROP) methods. Here, we present reversible-deactivation CROP of cyclic acetals using a commercial halomethyl ether initiator and an indium(III) bromide catalyst. Using this method, we synthesize poly(1,3-dioxolane) (PDXL), which demonstrates tensile strength comparable to some commodity polyolefins. Depolymerization of PDXL using strong acid catalysts returns monomer in near-quantitative yield and even proceeds from a commodity plastic waste mixture. Our efficient polymerization method affords a tough thermoplastic that can undergo selective depolymerization to monomer.

A characteristic optical variability time scale in astrophysical accretion disks

Gio, 12/08/2021 - 18:43

Accretion disks around supermassive black holes in active galactic nuclei produce continuum radiation at ultraviolet and optical wavelengths. Physical processes in the accretion flow lead to stochastic variability of this emission on a wide range of time scales. We measured the optical continuum variability observed in 67 active galactic nuclei and the characteristic time scale at which the variability power spectrum flattens. We found a correlation between this time scale and the black hole mass extending over the entire mass range of supermassive black holes. This time scale is consistent with the expected thermal time scale at the ultraviolet-emitting radius in standard accretion disk theory. Accreting white dwarfs lie close to this correlation, suggesting a common process for all accretion disks.