FIG. 1.

Transduction efficiencies of kissing-loop-modified vectors. The Akv kissing-loop sequence is shown at the top (underlined). Five kissing-loop-modified vector constructs, shown below the wild-type sequence, were generated. Deleted nucleotide positions are indicated by hyphens. Nucleotide substitutions within the loop motif (framed by broken lines) are indicated by boldface letters. Transduction titers were measured by counting the G418-resistant colonies appearing per milliliter of virus-containing medium transferred from stably transfected Ψ2 packaging cells to NIH 3T3 cells. Titers are based on five independent experiments performed with three independent sets of stably transfected cell lines. Standard deviations are indicated by error bars.