Structure of adeno-associated virus (AAV) vectors. The wild-type AAV consists of the viral genes rep and cap coding for the different rep (Rep78, Rep68, Rep52, Rep42) and cap (VP1, VP2, VP3) proteins, the AAV promoters (p5, p19, p40), the polyadenylation site (pA), and the inverted terminal repeats (ITR). In rAAV vectors, the viral rep and cap genes are replaced by a transgene cassette carrying the promoter, the transgene, and the pA site. (Redrawn from Walther and Stein 2000, with permission from Wolters Kluwer Pharma Solutions, Inc.)