Schmitt-Ulms, C. | bioRxiv Science

bioRxiv2022

RNA-triggered protein cleavage and cell death by the RNA-guided type III-E CRISPR-Cas nuclease-protease complex

The type III-E Cas7-11 effector nuclease forms a complex with a CRISPR RNA (crRNA) and the putative caspase-like protease Csx29, catalyzes crRNA-guided target RNA cleavage, and has been used for RNA targeting in eukaryotic cells. Here, we report cryo-electron microscopy structures of the Cas7-11-crRNA-Csx29 complex with and without target RNA, and demonstrate that target RNA binding induces a conformational change in Csx29 and results in the protease activation. Biochemical analysis confirmed that Cas7-11-bound Csx29 cleaves Csx30 in a target RNA-dependent manner. Reconstitution of the system in bacteria uncovered Csx30-dependent cellular toxicity regulated by Csx31, and that Csx29-mediated cleavage produces toxic Csx30 fragments, promoting cell death. We find that Csx30 can bind both Csx31 and the associated sigma factor RpoE, suggesting Csx30 can inhibit RpoE and modulate cellular stress response towards infection. Overall, the RNA-guided nuclease-protease activities of the Cas7-11-Csx29 effector complex facilitate protease-based programmed cell death.

molecular biology↗

bioRxiv2021

Drag-and-drop genome insertion without DNA cleavage with CRISPR-directed integrases

Programmable and multiplexed genome integration of large, diverse DNA cargo independent of DNA repair remains an unsolved challenge of genome editing. Current gene integration approaches require double-strand breaks that evoke DNA damage responses and rely on repair pathways that are inactive in terminally differentiated cells. Furthermore, CRISPR-based approaches that bypass double stranded breaks, such as Prime editing, are limited to modification or insertion of short sequences. We present Programmable Addition via Site-specific Targeting Elements, or PASTE, which achieves efficient and versatile gene integration at diverse loci by directing insertion with a CRISPR-Cas9 nickase fused to both a reverse transcriptase and serine integrase. Without generating double stranded breaks, we demonstrate integration of sequences as large as [~]36 kb with rates between 10-50% at multiple genomic loci across three human cell lines, primary T cells, and quiescent non-dividing primary human hepatocytes. To further improve PASTE, we discover thousands of novel serine integrases and cognate attachment sites from metagenomes and engineer active orthologs for high-efficiency integration using PASTE. We apply PASTE to fluorescent tagging of proteins, integration of therapeutically relevant genes, and production and secretion of transgenes. Leveraging the orthogonality of serine integrases, we engineer PASTE for multiplexed gene integration, simultaneously integrating three different genes at three genomic loci. PASTE has editing efficiencies comparable to or better than those of homology directed repair or non-homologous end joining based integration, with activity in non-dividing cells and fewer detectable off-target events. For therapeutic applications, PASTE can be delivered as mRNA with synthetically modified guides to programmably direct insertion of DNA templates carried by AAV or adenoviral vectors. PASTE expands the capabilities of genome editing via drag-and-drop gene integration, offering a platform with wide applicability for research, cell engineering, and gene therapy. One Sentence SummaryA new technology combining CRISPR-mediated genome editing and site-specific integrases enables efficient programmable gene integration at any targeted genomic locus without double-strand DNA breaks, leading to broad applications in basic science research, cell engineering, and gene therapy.

bioengineering↗