Infectivity of H89-NL4.3 and PKI-NL4.3. (A) Infectivity of normalized amounts of sucrose purified NL4.3, PKI-NL4.3 and H89-NL4.3 (10 ng p24 standardized to a final volume of 100 μL) was assayed in MAGIC-5B indicator cell lines. Control experiments consisted of mock infected cells (-) or NL4.3 infected cells maintained in the presence of 10 μM AZT. Infectivity was quantified by β-galactosidase activity in total cell lysate. Each value represents an average of three experiments performed in triplicate ± standard deviation. (B) Evaluation of viral samples contamination by co-purifying inhibitors. Supernatant (Sup.) of uninfected 293 cells maintained in medium alone (Mock) or cultured in the presence of H89 or Myr-PKI were subjected to gradient sucrose ultracentrifugation. Samples (100 μL) were then mixed with NL4.3 viruses (10 ng p24) produced from PKA proficient cells and the mixture was used to infect MAGIC-5B cells. Infectivity was measured as described in (A).