Quantification of intrinsic RT activity contained in NL4.3, H89-NL4.3 and PKI-NL4.3 particles. (A) Normalized amounts of sucrose-purified NL4.3, PKI-NL4.3 or H89-NL4.3 viruses were lysed and subjected to RT reaction in the presence of exogenous poly(A)/oligo dT template/primer hybrid and dNTPs. (B) RT reactions were performed with lysate of NL4.3 viruses incubated in the presence of H89 (100 μM) or Myr-PKI (50 μM) inhibitors. Addition of nevirapine (Nev) to the reaction mixture was used as a negative control. RT activity was quantified by ELISA as described in the Material and Methods section. Results are the mean of three separate experiments performed in triplicate ± standard deviation.