CRISPRassociated

CRISPR-associated proteins, or Cas proteins, are a diverse family of enzymes encoded in the genomes of bacteria and archaea that serve as the effector components of CRISPR immune systems. They use CRISPR RNAs to recognize and cleave invading genetic material, providing adaptive defense against phages and plasmids. Cas proteins form complexes with guide RNAs and, in some systems, with other RNA components to enable sequence-specific targeting.

CRISPR systems operate in three stages: adaptation, where new spacers derived from foreign DNA are integrated into the CRISPR array; expression and processing, where the array is transcribed and processed into mature guide RNAs; and interference, where the Cas effector cleaves matching DNA or RNA sequences adjacent to short motif requirements called PAMs. The result is targeted destruction of the invader while the host genome remains protected.

There are two major classes of CRISPR systems. Class 1 uses multi-subunit effector complexes, encompassing Types I, III, and IV. Class 2 uses a single, large Cas effector protein, including Types II, V, and VI. Notable examples include Cas9 (DNA targeting, Type II), Cas12 (DNA targeting with distinct PAM, Type V), Cas13 (RNA targeting with collateral RNA cleavage, Type VI), and Cas10 (a component of Type III systems with complex target recognition). These proteins vary in their mechanisms and nucleic acid preferences.

Applications of Cas proteins span genome editing, gene regulation, and biotechnology. Cas9 is widely used for targeted genome edits; Cas12 and Cas13 have contributed to diagnostic tools that detect nucleic acids through collateral cleavage activities. Ongoing research aims to discover new Cas enzymes, improve specificity and delivery, and expand the range of editable organisms and therapeutic possibilities.