Fig. 3

Fusion assay of alanine insertion mutants of gp41. a and b The DSP assay was performed at 2 h after coculture to examine the fusion activities of mutants. Surface expression levels of mutant Envs were determined by CELISA, and the fusion activity measured by the DSP assay (open bar) was normalized to the surface expression level (dark bar). Error bars represent the standard deviation of the results of triplicate experiments. The results for NHR and loop mutants are shown in a. b The results for CHR mutants. Statistical analysis was performed using t test. **p < 0.01 and *p < 0.05 when comparison of the indicated mutant with wild type was done. ns indicates no significant differences (p > 0.05) when 647+A and 648+A were compared. c Syncytia formation assays were used to evaluate the fusion activities of the mutants. The number of nuclei in the syncytia was divided by the total number of the nuclei in the field. Five randomly chosen fields were used to measure the value. The degree of syncytia formation is shown as a percentage (the wild-type was set as 100%). Statistical analysis was performed using t test. ns indicates no significant differences (p > 0.05) when compared with the value of the wild type