Analyses of the production and infectivity of viral particles. (A) Similar virus production from NL4-3 and deletion mutants. Culture supernatants of 293T cells transfected with the corresponding vectors were centrifuged through a 20% sucrose cushion. The amount of p24 in the virus pellets was determined and compared to the amount of p24 in the NL4-3 virus pellet, which was set at 100%. Means and SD of three independent experiments are shown. (B) NL4-3 and deletion mutants had similar protein expression and processing. Western blot analysis of HIV-1 virions with p24 or gp120 antiserum. The corresponding sizes of the HIV-1 proteins are shown to the right. (C) Infectious virus production varied among different mutants. Viruses harvested from the culture supernatant of 293T cells transfected with the corresponding vector were titrated for infectivity using the limiting dilution culture method in PM-1 cells. The TCID50 was calculated by the Reed and Muench method. The same aliquot of virus was quantified with p24 ELISA and used to normalize the titer of the virus stock. Means and SD of three independent experiments are shown. *, indicates p < 10-3 and significant deviation from the wild-type infectious virus titer as determined by Student's t test.