FIG. 8.

Theoretical model for HDEP formation. A specific head-to-head E1 coding sequence present in PER.C6 cells is incorporated into the Ad5 recombinant vector with E1 deleted via a nonhomologous recombination mechanism (top). The light gray arrow represents the FGF-4 coding sequence, and solid black boxes represent the ITRs. The genomic fragment from PER.C6 cells (shaded box) contains three full copies of the E1 plasmid (long black arrows in shaded box) and two partial E1 plasmid sequences (small black arrows in shaded box). The location of the sequence inversion point is represented by a small white box. Recombination events, illustrated by the crosses, can result in HDEP genomes of 37 or 30 kb, depending on where recombination takes place. The reciprocal molecules are too large to be packaged.