KREUZADER (Posts tagged biology)

Disabling Cas9 by an anti-CRISPR DNA mimic
“CRISPR (clustered regularly interspaced short palindromic repeats)–Cas9 gene editing technology is derived from a microbial adaptive immune system, where bacteriophages are often the intended target.... — Disabling Cas9 by an anti-CRISPR DNA mimic
CRISPR (clustered regularly interspaced short palindromic repeats)–Cas9 gene editing technology is derived from a microbial adaptive immune system, where bacteriophages are often the intended target. Natural inhibitors of CRISPR-Cas9 enable phages to evade immunity and show promise in controlling Cas9-mediated gene editing in human cells. However, the mechanism of CRISPR-Cas9 inhibition is not known, and the potential applications for Cas9 inhibitor proteins in mammalian cells have not been fully established. We show that the anti-CRISPR protein AcrIIA4 binds only to assembled Cas9–single-guide RNA (sgRNA) complexes and not to Cas9 protein alone. A 3.9 Å resolution cryo–electron microscopy structure of the Cas9-sgRNA-AcrIIA4 complex revealed that the surface of AcrIIA4 is highly acidic and binds with a 1:1 stoichiometry to a region of Cas9 that normally engages the DNA protospacer adjacent motif. Consistent with this binding mode, order-of-addition experiments showed that AcrIIA4 interferes with DNA recognition but has no effect on preformed Cas9-sgRNA-DNA complexes. Timed delivery of AcrIIA4 into human cells as either protein or expression plasmid allows on-target Cas9-mediated gene editing while reducing off-target edits. These results provide a mechanistic understanding of AcrIIA4 function and demonstrate that inhibitors can modulate the extent and outcomes of Cas9-mediated gene editing.

Source: advances.sciencemag.org

crispr-cas9 genetic engineering biology medicine

Perchlorates on Mars enhance the bacteriocidal effects of UV light“Perchlorates have been identified on the surface of Mars. This has prompted speculation of what their influence would be on habitability. We show that when irradiated with a simulated... — Perchlorates on Mars enhance the bacteriocidal effects of UV light
Perchlorates have been identified on the surface of Mars. This has prompted speculation of what their influence would be on habitability. We show that when irradiated with a simulated Martian UV flux, perchlorates become bacteriocidal. At concentrations associated with Martian surface regolith, vegetative cells of *Bacillus subtilis* in Martian analogue environments lost viability within minutes. Two other components of the Martian surface, iron oxides and hydrogen peroxide, act in synergy with irradiated perchlorates to cause a 10.8-fold increase in cell death when compared to cells exposed to UV radiation after 60 seconds of exposure. These data show that the combined effects of at least three components of the Martian surface, activated by surface photochemistry, render the present-day surface more uninhabitable than previously thought, and demonstrate the low probability of survival of biological contaminants released from robotic and human exploration missions.

Source: nature.com

mars biology chemistry

New study reveals key steps in CRISPR-Cas3 function at near-atomic resolution“CRISPR-Cas3 is a subtype of the CRISPR-Cas system, a widely adopted molecular tool for precision gene editing in biomedical research. Aspects of its mechanism of action,... — New study reveals key steps in CRISPR-Cas3 function at near-atomic resolution
CRISPR-Cas3 is a subtype of the CRISPR-Cas system, a widely adopted molecular tool for precision gene editing in biomedical research. Aspects of its mechanism of action, however, particularly how it searches for its DNA targets, were unclear, and concerns about unintended off-target effects have raised questions about the safety of CRISPR-Cas for treating human diseases.
Harvard Medical School and Cornell University scientists have now generated near-atomic resolution snapshots of CRISPR that reveal key steps in its mechanism of action. The findings, published in Cell on June 29, provide the structural data necessary for efforts to improve the efficiency and accuracy of CRISPR for biomedical applications.
Through cryo-electron microscopy, the researchers describe for the first time the exact chain of events as the CRISPR complex loads target DNA and prepares it for cutting by the Cas3 enzyme. These structures reveal a process with multiple layers of error detection—a molecular redundancy that prevents unintended genomic damage, the researchers say.

Source: hms.harvard.edu

biology genetic engineering crispr-cas3 crispr

This video shows replication of individual pieces of double stranded DNA. This is the first time individual steps in DNA replication – arguably, the fundamental process of life on Earth – have been observed directly. Each glowing strand is a piece of double helix growing by replication at the left-hand end. They move at different speeds and stop and start. Dark gaps in the line are single-stranded DNA where one polymerase failed to attach (the fluorescent dye only binds double-stranded DNA).

Source: ucdavis.edu

biology dna