S. aureus CBE N-terminal Fragment

N-terminal fragment of SaCas9-based cytosine editor split via Npu intein at Lys534. Compact size enables efficient AAV packaging.

Length: 1000 bp (333 aa)

Type: Cytosine Base Editor

Conversion: C-to-T

Origin: Rat APOBEC1 fused to S. aureus Cas9 D10A nickase (amino acids 1-534)

Characteristics

Contains rat APOBEC1 cytosine deaminase domain and N-terminal portion of SaCas9 D10A (residues 1-534). SaCas9 provides ~1 kb size reduction versus SpCas9, enabling more efficient AAV packaging. Split site at Lys534 positions Npu intein for protein trans-splicing. Recognizes NNGRRT PAM. Expresses from Cbh promoter in reference AAV construct.

Applications

Compact dual-delivery cytosine base editing systems where smaller size facilitates AAV packaging and co-transduction. Compatible with engineered AAV serotypes for diverse tissue targeting. Validated for brain, liver, and retina editing in mice. Can be adapted to other delivery platforms when paired with C-terminal fragment.

Limitations

Non-functional without C-terminal pair. NNGRRT PAM more restrictive than SpCas9 NGG, limiting targeting scope. Dual-AAV system requires co-transduction for reconstitution. Must be co-delivered with split-sacbe-ct for C-to-T editing activity.

Literature References

  1. Komor et al. (2016). Programmable editing of a target base in genomic DNA without double-stranded DNA cleavage. Nature - Komor 2016 BE3
  2. Levy et al. (2020). Cytosine and adenine base editing of the brain, liver, retina, heart and skeletal muscle of mice via adeno-associated viruses. Nat Biomed Eng - Levy 2020 BE3.9max