Western blot analysis of expression and incorporation of gp120 and gp41 in the viral envelope of WT and mutant gp41 virus strains. A. Analysis of the levels of gp120 and gp41 incorporation in virus particles. P24 was added to ascertain an equal-loading of the samples. M: MagicMark XP Western protein standard (Novex). All 3 panels are part of the same original blot (Additional file 1: Figure S1). B. Relative protein levels as quantified based on panel A using the ImageJ software, presented as normalized to p24 levels. Data are the means ± SEM of at least 5 independent experiments. The difference between WT and mutant virus was considered to be significant when the p value calculated using the student’s t-test was <0.05 (* = p < 0.05, ** = p < 0.005).