CRISPR-Cas systems are found widely in prokaryotes, where they provide adaptive immunity against virus infection and plasmid transformation. In July 2020, team of Jennifer Doudna from University of California described a minimal functional CRISPR-Cas system, comprising a single ~70-kilodalton protein, CasΦ, and a CRISPR array, encoded exclusively in the genomes of huge bacteriophages.
CasΦ uses a single active site for both CRISPR RNA (crRNA) processing and crRNA-guided DNA cutting to target foreign nucleic acids. This hypercompact system is active in vitro and in human and plant cells with expanded target recognition capabilities relative to other CRISPR-Cas proteins.
Useful for genome editing and DNA detection but with a molecular weight half that of Cas9 and Cas12a genome-editing enzymes, CasΦ offers advantages for cellular delivery that expand the genome editing toolbox.