Simple explanation
The biggest practical problem in gene editing is not the editing, it is getting the machinery into the right cells. The most common delivery vehicle, a modified virus, has a strict luggage limit, and Cas9 barely fits. Cas14 and its relatives are miniature versions of the same kind of enzyme — small enough to leave room for everything else you need to pack.
Go deeper
Cas14 proteins (reclassified within Cas12f) are compact type V effectors of roughly 400–700 amino acids, discovered in uncultivated archaea. CasΦ (Cas12j), found in huge bacteriophages, is similarly small and notable for recognising a minimal T-rich PAM and processing its own guide RNA. Their size makes them attractive for AAV delivery, where the ~4.7 kb packaging limit is a hard constraint; native activity in human cells is generally lower than SpCas9 and much of the work is engineering to improve it.
Why size is the point
Adeno-associated virus, the workhorse of in vivo gene delivery, cannot carry more than about 4.7 kilobases. SpCas9 alone consumes most of that budget before you add a promoter, a guide and any regulatory sequence. A nuclease a third the size changes what is possible to deliver in a single vector — which is why an enzyme with modest laboratory activity still attracts serious engineering effort.
Where it stands
These are research-stage tools. They are used in laboratories and are being engineered for higher activity, and no therapeutic programme based on them has reached the clinic.
Sources
- Science (Harrington et al.) · 2018
CRISPR-Cas14 is a family of miniature RNA-guided nucleases ↗ - Science (Pausch et al.) · 2020
CRISPR-CasΦ from huge phages is a hypercompact genome editor ↗