Syn-FLEX-NES-jRGECO1a AAV (Serotype 9)

Adeno-associated virus (AAV) is a small (25 nm) virus belonging to the Parvoviridae family that consists of a non-enveloped icosahedral capsid (protein coat) containing a linear single-stranded DNA genome of approximately 4.7 kb. The AAV genome encodes multiple protein products, namely four nonstructural Rep proteins, three capsid proteins (VP1-3), and the recently discovered assembly activation protein (AAP). The AAV gene is essential for its biological cycle and is flanked by two AAV-specific palindromic inverted terminal repeats (ITRs; 145 bp). AAV viruses can infect both dividing and non-dividing cells and remain latent in host cell DNA by integrating into a specific chromosomal site (the adeno-associated virus integration site [AAVS]) unless a helper virus provides it with replication functions.

In the genome of recombinant AAV vectors used for gene therapy, the two ITRs (viral genome cis-packaging signals) are retained, while other viral sequences (e.g., rep and cap genes) are exchanged with the foreign DNA of choice. The target DNA flanking the AAV ITR is often referred to as the "transgene expression cassette." Infection and transduction of cells by AAV vectors occur through a series of sequential events as follows: interaction of the viral capsid with receptors on the surface of the target cell, internalization by endocytosis, intracellular trafficking through endocytic/proteasomal compartments, endosomal escape, nuclear import, virion uncoating, and viral DNA double-strand conversion, leading to transcription and expression of the transgene. The conversion of the AAV genome from single-stranded DNA to double-stranded DNA occurs through two pathways: (1) de novo synthesis of complementary DNA strands (second-strand synthesis) and (2) base pairing of complementary single-stranded AAV genomes from different AAV viruses co-infecting the same cell (strand annealing).