The absence of pVII does not preclude virus particle assembly and genome packaging.

<p>(A) CsCl equilibrium gradient centrifugation of virus particles isolated from isolated from 293 cells (Cre<sup>–</sup>) or 293 cells expressing Cre recombinase (Cre<sup>+</sup>) infected with the Ad5-VII-loxP virus. Virus particles from both infections banded on the gradient at 1.34 g/cc, the density of mature Ad5 virions. (B) Electron microscopy images of negative stained CsCl-purified virions isolated from 293 cells (Cre<sup>–</sup>) or 293 cells expressing Cre recombinase (Cre<sup>+</sup>) infected with wild-type Ad5 (WT) or the Ad5-VII-loxP virus. Bar inset represents 50nm. (C) Coomassie blue stain analysis of the protein composition of CsCl-purified virions isolated from 293 cells infected with wild-type Ad5 (WT) or the Ad5-VII-loxP virus (VII<sup>+</sup>) or 293 cells expressing Cre recombinase (VII<sup>–</sup>) infected with the Ad5-VII-loxP virus. Virus particles from the Ad5-VII-loxP-infected cells were harvested 48 and 72 hr post-infection (hpi). Protein molecular weight markers are indicated on the left. Major Ad capsid proteins are indicated on the right. (D) Western blot analyses of purified virus particles described in (C). Ad capsid proteins are indicated on the right. (E) Western blot analysis of purified virus particles described in (C), plus <i>ts</i>1 particles isolated following infection of cells at the restrictive temperature, probed with antibodies directed against pVI/VI, or C-terminal peptides of pVI (VI-C) or pVIII (VIII-C). The asterisk (*) indicates full-length, unprocessed pre-VI, the bullet (•) indicates iVI, and the open circle (o) indicates fully processed VI.</p>