How do Cas12 and Cas13 differ from Cas9 in their mechanisms and applications?

Cas12a (Cpf1) targets DNA with a T-rich PAM (TTTV), uses a single crRNA (no tracrRNA), creates staggered cuts producing sticky ends, and has collateral ssDNA cleavage activity useful for diagnostics (DETECTR). Cas12b offers similar features with different PAM preferences. Cas13 targets RNA rather than DNA, enabling transcriptome editing, RNA knockdown (alternative to RNAi), and diagnostic applications (SHERLOCK using collateral ssRNA cleavage). Cas13 knockdown is reversible and doesn't alter genome. Applications include RNA editing (using dCas13-ADAR fusions), viral RNA detection, and transcript modulation. Each system expands the CRISPR toolkit for different research and therapeutic needs.