Biotechnology Genetics

Scientists find new and smaller CRISPR gene editor: CasX


For the last seven years, scientists were considering Cas9 to be a vital but a formidable gene editor. As it was an easy known and versatile that could be used in animals, plants, humans, and bacteria. Its accuracy and precision in gene editing are remarkable, transforming biology and would open new possibilities for diseases treatment.

But, this new baby in the family, CasX, may run Cas9 out of the league.

CasX, discovered two years ago by the University of California, Berkeley scientists Jill Banfield and Jenifer Doudna while working on the same bacteria, where she discovered Cas9. You can consider it a Cas9’s twin but smaller in size. Its small size can make it a better option while delivering the gene editing tool (CRISPR) into a cell.

But would it work outside its native bacteria?

A recent study published in Nature, this new Cas protein – CasX, is considered to be a more effective and potent gene editor for both bacterial and human cells.

Similarities with other Cas proteins

  • Its structure is the same as that of Cas9 and Cas12.
  • Cutting both the strand of DNA just like Cas9.
  • Can perform gene editing by binding to a specific target sequence of DNA like Cas9.

What makes CasX a better option?

Synthetic biology and gene editing are a perceptive study which involves a complete accuracy. The properties that CasX possess, make it a better option:

  • It usually evolves from a different region of the bacterial genome, which is independent of the parts that code for other Cas proteins.
  • Its size is tiny as compared to other Cas family proteins.
  • It can quickly tackle the human immune system because the bacteria that produce it is usually not present in humans.
crispr casX
“A new gene-editing protein, CasX, may give CRISPR-Cas9 a run for its money. UC Berkeley scientists have determined the unique structure of CasX (grey), revealing that this pint-sized Cas enzyme is dominated by RNA (red) that directs it to specific sequences of DNA (blue), where it binds and cuts the DNA.” Credit: University of California – Berkeley


“The immunogenicity, delivery, and specificity of a genome-editing tool are all vitally important.” Said co-lead author Benjamin Oakes.

Co-authors of the study Jun-Jie Liu and Natalia Orlova utilized a cryo-electron microscope and revealed the snapshots of the CasX protein while editing a gene. It was also showing its unmatched molecular activity as compared to other Cas proteins. And concluded that it evolved independently, sharing no common ancestor with Cas9.

“The first thing that jumps out is how the highly unique domains accomplish similar roles to what we have seen with other RNA-guided DNA-binding proteins. CasX’s minimal size, with no fat on the bone, helps to demonstrate there is a basic recipe that nature uses clearly,” says Oakes. “Understanding this recipe will help us to better evolve and engineer genome editing tools for our purposes rather than nature’s,” he added.

“We aren’t just looking to uncover the next pair of molecular scissors. We want to build the next Swiss Army knife,” said Jennifer Doudna, the co-founder of CRISPR, and a UC Berkeley professor of molecular and cell biology.


Explore more: Cloned Gene-Edited Monkeys with Horrifying Results

More information: Jun-Jie Liu et al. CasX enzymes comprise a distinct family of RNA-guided genome editors, Nature (2019). DOI: 10.1038/s41586-019-0908-x

Journal reference: Nature

Provided by: University of California – Berkeley

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