A Tiny Cas Made by Huge Phages

Cas-phi has been discovered in huge phages

Basem Al-Shayeb and Patrick Pausch are researchers from UC Berkeley that are part of Jennifer Doudna's lab group. The researchers found that huge phages encode a tiny Cas called Cas Φ (Cas-Phi), their work has been published in Science.

The CRISPR-Cas system was discovered in bacteria as a defence mechanism against invading phages. Now the CRISPR Cas system has been found in large phages too. The researchers found that these huge phages encode CRISPR-Cas systems in their DNA sequences. The huge phages bind to and inject their DNA into the bacterial host, and then the host bacteria produces CasΦ. The researchers believe that CasΦ is used to destroy phages that are directly competing with the large phage for the bacterial host. The researchers from UC Berkeley also tested whether CasΦ could be used for gene editing purposes like Cas9. CasΦ was able to conduct gene-editing in plant and human cells, and it can cause a double-stranded break in DNA which is similar to how Cas9 works.

“This study shows that this virus-encoded CRISPR-Cas protein is actually very good at what it does, but it is a lot smaller, about half the size of Cas9,” said Jennifer Doudna, one of the pioneers of CRISPR. It would be beneficial to use CasΦ for gene-editing purposes, as delivering the CRISPR-Cas components can be a hurdle due to the large size of Cas9 and the limited delivery capacity. Therefore, using CasΦ may help to overcome the delivery issues due to the compact nature of CasΦ. This fascinating discovery by UC Berkeley has further widened the CRISPR tool kit and may help to advance CRISPR further than ever!

Tiny MIghty CasPhi Gene-Editing - UC Berkeley

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References: https://science.sciencemag.org/content/369/6501/333.full