CPP and infection: For AAV2, it has been proposed that processing through endosomal compartments, including early and late endosomes,9,34,35 is required to induce a conformational rearrangement of the viral capsid for nuclear transport and uncoating.36 To investigate whether the endosomal environments are required for productive infection of AAV2-CPP complexes, bafilomycin A1, which specifically inhibits vacuolar proton ATPases,37 was used to block low pH-associated endosomal processes in cells.