The smallest Cas9 genetic scissors (so far)

Scientists at the Center for Genome Engineering, within the Institute for Basic Science (IBS), in collaboration with KIM Eunji (ToolGen Inc.) and KIM Jeong Hun (Seoul National University) have engineered the smallest CRISPR-Cas9 to date, delivered it to the muscle cells and in the eyes of mice via adeno-associated viruses (AAV) and used it to modify a gene causing blindness. 

Published on Nature Communications, this CRISPR-Cas9 system, originated from Campylobacter jejuni (CjCas9), is expected to become a useful therapeutic tool against common and "undruggable" disease targets.

CRISPR-Cas9 is the buzzword amongst molecular biologists. It is an innovative, cheap and precise technique to edit genes. Cas9 is the "gene scissors" protein: It creates cuts on the target gene in precise locations indicated by the guide RNA.

In order for CRISPR-Cas9 complex to reach the target DNA, it has to be delivered via plasmids or viruses. "AAV is an efficient and safe vector to express a gene of interest in vivo and has been used widely in gene therapy," explains KIM Jin-Soo, director of the IBS Center for Genome Engineering and corresponding author of the study.

The most common version of the CRISPR-Cas9 technique uses Cas9 derived from the bacterium Streptococcus pyogenes. However, this protein is made of 1,368 aminoacids and it is too large to be delivered and packaged in AAV.

In this study, the team found that CjCas9 is both efficient and small. It has 984 aminoacids and it can be packed in AAV together with more than one guide RNAs as well as with a fluorescent reporter protein.