For ssAAV vectors, the coding sequence and complementary sequence of the transgene expression cassette are on separate strands and are packaged in separate viral capsids. For scAAV vectors, both the coding and complementary sequence of the transgene expression cassette are present on each plus-and minus-strand genome. The black lines represent sequences in the bacterial backbone; the blue and red lines represent sequences of the coding and complementary sequence of the transgene expression cassette, respectively.

Graphical representation of the difference between conventional ssAAV and scAAV vectors.

DNA rescue and transduction of a conventional single-stranded AAV (ssAAV) and a self-complementary AAV (scAAV) vector. Full-length ssAAV vector genome of both polarities are rescued from the vector plasmid and individually packaged into the AAV capsids. As a genome conversion in the transduced cell nucleus, the single-to-double stranded conversion of the DNA goes through the inter-molecular annealing or second strand synthesis. In contrast, a scAAV vector with half the size of the ssAAV genome has a mutation in the terminal resolution site (TRS) to form a vector genome with wild-type ITRs at the both ends and mutated ITR at the center of symmetry. After uncoating in the target cell nucleus, this DNA structure can readily fold into transcriptionally active double-stranded form through intra-molecular annealing.