Time will tell if it is going to become the preferred enzyme for genome editing or just another useful tool in the expanding CRISPR kit. But the future of CasX looks bright. It is much smaller than the nucleases that have provided a foundation for this technology. Being fewer than a thousand amino acids, it offers clear advantages for delivery in comparison with Cas9, that is over 1,300 Aa.

The analysis by Jennifer Doudna et al. published in Nature today shows it has structural features and functional mechanisms not found in other Cas proteins but is capable of modifying the genomes of both humans and bacteria.

Its origin story is also interesting, as CasX comes from an uncultivated microbe isolated from groundwater through metagenomics search.

Only two weeks ago Cas9 found another competitor in BhCas12b, a Cas protein from Bacillus hisashii engineered to operate at lower temperatures. Experts agree that more digging into microbial diversity will probably provide further gems.