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Table 1 Contrasting characteristics of the four standard nuclease platforms

From: Towards a new era in medicine: therapeutic genome editing

Nuclease Target site length Mechanism of recognition First use in human cells Ease of design Number of components Size of mRNA transcript
Engineered meganuclease >18 bp Protein-DNA 1994 (I-SceI) Extremely difficult 1 Short
Zinc-finger nuclease 18–36 bp Protein-DNA 2003 Difficult 2 Short
TAL effector nuclease 24–40 bp Protein-DNA 2011 Easy 2 Long
CRISPR/Cas9 nuclease 19–22 bp (Streptococcus pyogenes Cas9) RNA-DNA Watson-Crick base-pairing 2013 Simple 1 (if using a complex guide RNA with Cas9 protein) or Long
2 (if delivering guide RNA and Cas9 separately)