Poly-L-lysine's enhancement of virus transduction is size dependent. (A) Ecotropic virus was supplemented with concentrations of 1–4-kDa (solid circles), 4–15-kDa (open circles), or 15–30-kDa (solid squares) poly-L-lysine. NIH-3T3 cells were exposed to the virus samples for 48 h, and transduction was measured via the ONPG assay. (B) Ecotropic virus was supplemented with concentrations of 30–70-kDa (solid circles), 70–150-kDa (open circles), 150–300-kDa (solid squares), or >300-kDa (open squares) poly-L-lysine. NIH-3T3 cells were exposed to the virus samples for 48 h, and transduction was measured via the ONPG assay.