Transduction by AAV vectors. The different steps required for transduction by AAV vectors are indicated, including an initial interaction with a variety of possible receptor and coreceptor molecules on the cell surface, virion internalization, nuclear entry and release of the single-stranded vector genomes, followed by second-strand DNA synthesis, hybridization of complementary input genomes, and/or chromosomal integration before gene expression can occur from a double-stranded template. Potential secondary structures of episomal vector genomes are shown, as are vector-encoded RNA molecules (bent arrows). Question marks indicate a lack of detailed understanding of the particular step involved. For further details see main text.