Complex dependence of CRISPR-Cas9 binding strength on guide RNA spacer lengths

Temperature dependent in vitro binding and release of target DNA by Cas9 enzyme

The CRISPR-associated protein 9 (Cas9) system has proven to be a powerful technology for genome editing in a wide variety of in vivo and in vitro applications. CRISPR-Cas9, when loaded with the guide RNA, cleaves the DNA at the target position as recognized by the guide RNA sequence. For successful application of this technology, it is important to study the biophysical parameters affecting its function. Temperature dependence of the Cas9 binding as well as energetics of product release after cleavage has not been well reported in the literature. In this work, we study the binding properties of Cas9 enzyme to the sequence specific target DNA at a range of temperatures and, surprisingly, find that the Cas9 enzyme, in our study, can find and bind its target DNA with 90 ± 20% efficiency at temperatures as low as 4 °C. Further, we show that the cleaved DNA products remain bound to the Cas9 enzyme strongly and is released from the enzyme only at higher temperatures. Using the gel shift assays, we quantify the rate of Cas9 binding to target DNA to be 0.8 ± 0.2 min-1 at 37 °C. We also tested denaturant (SDS) dependent release of cleaved product which showed a similar release pattern with a dissociation constant of 0.23 ± 0.04 mM. Our results of heat and denaturant dependence on Cas9-DNA binding and release mechanics will provide valuable insights for developing temperature dependent applications of the CRISPR-Cas9 technology.

Rapid cell-free characterization of multi-subunit CRISPR effectors and transposons

CRISPR-Cas biology and technologies have been largely shaped to date by the characterization and use of single-effector nucleases. By contrast, multi-subunit effectors dominate natural systems, represent emerging technologies, and were recently associated with RNA-guided DNA transposition. This disconnect stems from the challenge of working with multiple protein subunits in vitro and in vivo. Here, we apply cell-free transcription-translation (TXTL) systems to radically accelerate the characterization of multi-subunit CRISPR effectors and transposons. Numerous DNA constructs can be combined in one TXTL reaction, yielding defined biomolecular readouts in hours. Using TXTL, we mined phylogenetically diverse I-E effectors, interrogated extensively self-targeting I-C and I-F systems, and elucidated targeting rules for I-B and I-F CRISPR transposons using only DNA-binding components. We further recapitulated DNA transposition in TXTL, which helped reveal a distinct branch of I-B CRISPR transposons. These capabilities will facilitate the study and exploitation of the broad yet underexplored diversity of CRISPR-Cas systems and transposons.

An Outlook on Global Regulatory Landscape for Genome-Edited Crops

The revolutionary technology of CRISPR/Cas systems and their extraordinary potential to address fundamental questions in every field of biological sciences has led to their developers being awarded the 2020 Nobel Prize for Chemistry. In agriculture, CRISPR/Cas systems have accelerated the development of new crop varieties with improved traits-without the need for transgenes. However, the future of this technology depends on a clear and truly global regulatory framework being developed for these crops. Some CRISPR-edited crops are already on the market, and yet countries and regions are still divided over their legal status. CRISPR editing does not require transgenes, making CRISPR crops more socially acceptable than genetically modified crops, but there is vigorous debate over how to regulate these crops and what precautionary measures are required before they appear on the market. This article reviews intended outcomes and risks arising from the site-directed nuclease CRISPR systems used to improve agricultural crop plant genomes. It examines how various CRISPR system components, and potential concerns associated with CRISPR/Cas, may trigger regulatory oversight of CRISPR-edited crops. The article highlights differences and similarities between GMOs and CRISPR-edited crops, and discusses social and ethical concerns. It outlines the regulatory framework for GMO crops, which many countries also apply to CRISPR-edited crops, and the global regulatory landscape for CRISPR-edited crops. The article concludes with future prospects for CRISPR-edited crops and their products.

An Outlook on Global Regulatory Landscape for Genome-Edited Crops

The revolutionary technology of CRISPR/Cas systems and their extraordinary potential to address fundamental questions in every field of biological sciences has led to their developers being awarded the 2020 Nobel Prize for Chemistry. In agriculture, CRISPR/Cas systems have accelerated the development of new crop varieties with improved traits—without the need for transgenes. However, the future of this technology depends on a clear and truly global regulatory framework being developed for these crops. Some CRISPR-edited crops are already on the market, and yet countries and regions are still divided over their legal status. CRISPR editing does not require transgenes, making CRISPR crops more socially acceptable than genetically modified crops, but there is vigorous debate over how to regulate these crops and what precautionary measures are required before they appear on the market. This article reviews intended outcomes and risks arising from the site-directed nuclease CRISPR systems used to improve agricultural crop plant genomes. It examines how various CRISPR system components, and potential concerns associated with CRISPR/Cas, may trigger regulatory oversight of CRISPR-edited crops. The article highlights differences and similarities between GMOs and CRISPR-edited crops, and discusses social and ethical concerns. It outlines the regulatory framework for GMO crops, which many countries also apply to CRISPR-edited crops, and the global regulatory landscape for CRISPR-edited crops. The article concludes with future prospects for CRISPR-edited crops and their products.

An Outlook on Global Regulatory Landscape for Genome-Edited Crops

The revolutionary technology of CRISPR/Cas systems and their extraordinary potential to address fundamental questions in every field of biological sciences has led to their developers being awarded the 2020 Nobel Prize for Chemistry. In agriculture, CRISPR/Cas systems have accelerated the development of new crop varieties with improved traits-without the need for transgenes. However, the future of this technology depends on a clear and truly global regulatory framework being developed for these crops. Some CRISPR-edited crops are already on the market, and yet countries and regions are still divided over their legal status. CRISPR editing does not require transgenes, making CRISPR crops more socially acceptable than genetically modified crops, but there is vigorous debate over how to regulate these crops and what precautionary measures are required before they appear on the market. This article reviews intended outcomes and risks arising from the site-directed nuclease CRISPR systems used to improve agricultural crop plant genomes. It examines how various CRISPR system components, and potential concerns associated with CRISPR/Cas, may trigger regulatory oversight of CRISPR-edited crops. The article highlights differences and similarities between GMOs and CRISPR-edited crops, and discusses social and ethical concerns. It outlines the regulatory framework for GMO crops, which many countries also apply to CRISPR-edited crops, and the global regulatory landscape for CRISPR-edited crops. The article concludes with future prospects for CRISPR-edited crops and their products.