Smallest life forms have smallest working CRISPR system

An ancient group of microbes that contains some of the smallest life forms on Earth also has the smallest CRISPR gene-editing machinery discovered to date.

The peewee protein machinery, dubbed Cas14, is related to but one-third the size of the Cas9 protein, the business end of the revolutionary gene-editing tool CRISPR-Cas9. While Cas9 was isolated from bacteria, Cas14 was found in the genome of a group of Archaea – a primitive relative of bacteria – that contains some of the smallest cells and smallest genomes known.

Cas9 and other Cas proteins are part of a defense system evolved by microbes to protect themselves from viruses. All are targeted enzymes that seek out and bind very selectively to a specific DNA or RNA sequence – in microbes, those that match sequences stored in its CRISPR memory banks after earlier viral infections – and then cuts the DNA or RNA to disable the new invader.

Like Cas9, Cas14 has potential as a biotech tool. Because of its small size, Cas14 could be useful in editing genes in small cells or in some viruses. But with its single-stranded DNA cutting activity, it is more likely to improve rapid CRISPR diagnostic systems now under development for infectious diseases, genetic mutations and cancer.

"For molecular diagnostics, you want to be able to target double-stranded DNA, single-stranded DNA and RNA," said Lucas Harrington, a UC Berkeley graduate student and first author of a paper reporting the discovery. "Cas12 is really good at double-stranded DNA recognition, Cas13 is really good at single-stranded RNA recognition and now Cas14 completes the set: it is really good at single-stranded DNA recognition."