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Researchers were unaware that they had come onto a ground-breaking technique that would allow them to alter the DNA of live cells when they figured out how bacteria defend themselves against viral invaders known as phages in the early 2000s.

By storing genetic segments of the invader, known as spacers, the mechanism, known as CRISPR, is incorporated into the genome of bacteria and allows them to “remember” previous viral infections.

These stored memories are then translated into small RNA guides in the most well-known variant of the system, CRISPR-Cas9, which equips the Cas9 protein to function as a weapon and cut up the invader the next time the bacteria come into contact with a corresponding phage.

In order to initiate its attack, Cas9 also uses a small DNA marker known as a PAM, which refers to “can cut here.”

CRISPR-Cas9 has been used by researchers to modify human and animal cells in order to create gene therapies. However, one crucial aspect of the CRISPR-Cas9 system’s function has remained unclear: What is the process by which bacteria create new immunological memories?

A widely held belief about Cas9 has been disproved by the researchers: that the “empty” or apo form of Cas9 is useless when it is not attached to its typical RNA partners. Nature is the publication where their work was published.

Read more…..https://phys.org/news/2025-09-crispr-reveals-role-cas9-guardian.html

Sources:

CRISPR study reveals surprising role of Cas9 as guardian of bacterial defense. https://phys.org/news/2025-09-crispr-reveals-role-cas9-guardian.html

Xufei Zhou et al. (2025). Cas9 senses CRISPR RNA abundance to regulate CRISPR spacer acquisition, Nature. DOI: 10.1038/s41586-025-09577-9

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