AAV8 SaCas9

Adeno-Associated Virus serotype 8 (AAV8) was isolated from rhesus monkey tissue, and the AAV8 rep and cap nucleotide sequences have 88% homology with AAV7 and 82% with AAV2. AAV8 exhibits greater transduction efficiency in the liver than other AAV serotypes. AAV8 and 9 have recently been used to correct disease-causing mutations and improve muscle function in mouse models of Duchenne muscular dystrophy. Cas9 is an endonuclease enzyme that introduces a double stranded break into the DNA when recruited to a specific DNA sequence by the sgRNA (single guide RNA). This double stranded break is repaired in mammalian cells either through Non-Homologous End Joining or Homologous Recombination. Non-Homologous End Joining often results in the deletion or insertion of several base pairs at the cut site, which, when resulting in a frameshift, causes the functional inactivation of the gene. SaCas9 (Staphylococcus aureus CRISPR-associated protein 9) has demonstrated high cutting efficiency in mammalian cells, and its smaller size makes it ideal for packaging into AAV. SaCas9 recognizes a longer protospacer adjacent motif (PAM) site, 5'-NNGRRT-3', than the more traditional SpCas9 (Streptococcus pyogenes CRISPR-associated protein 9). These AAV particles constitutively express SaCas9 under the control of a CMV promoter.