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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)