S. aureus BE3.9max N-terminal Fragment
N-terminal fragment of optimized SaCas9 base editor split via Npu intein at Lys534. Combines compact size with enhanced expression.
Origin: Codon-optimized APOBEC1 with enhanced NLS, fused to S. aureus Cas9 D10A nickase (amino acids 1-534)
Characteristics
Contains codon-optimized APOBEC1 with enhanced nuclear localization signals and N-terminal portion of SaCas9 D10A (residues 1-534). BE3.9max optimizations provide higher editing efficiency through improved nuclear import and expression. SaCas9 compact size enables efficient AAV packaging. Recognizes NNGRRT PAM. Expresses from Cbh promoter in reference AAV construct.
Applications
High-efficiency compact dual-delivery cytosine base editing. Particularly effective in hard-to-transduce tissues requiring compact editors. Validated in brain, liver, retina, heart, and skeletal muscle with up to 59% editing. 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. Total coding sequence approaches AAV packaging limits. Requires optimization of AAV dose and serotype for each target tissue. Must be co-delivered with split-sabe39max-ct for C-to-T editing activity.
Literature References
- Komor et al. (2016). Programmable editing of a target base in genomic DNA without double-stranded DNA cleavage. Nature - Komor 2016 BE3
- Komor et al. (2017). Improved base excision repair inhibition and bacteriophage Mu Gam protein yields C:G-to-T:A base editors with higher efficiency and product purity. Sci Adv - Komor 2017 BE4
- Koblan et al. (2018). Improving cytidine and adenine base editors by expression optimization and ancestral reconstruction. Nat Biotechnol - Koblan 2018 BE4max
- 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