FIG. 1.

DNA structure of helper-dependent vectors. To confirm the molecular structure of the viral particles, DNA was isolated and digested with the restriction enzyme BamHI. Bands corresponding to the pattern of helper H14 DNA were barely seen in the vectors, suggesting the level of helper contamination was low. Vector gAd.Alb-mal1 had slightly higher levels of H14 because its expression cassette is approximately 3 kb larger than the shRNA cassette, resulting in a construct with a DNA molecular mass closer to that of the helper (∼31 and 36 kb, respectively). After isopycnic centrifugation the vector and helper bands were closer, making collection of the helper-dependent vector band more difficult.