Virions produced by wild-type and bm Gag accumulate at the outer surface of the PM in primary B cells. (A) HEK293 cells were transfected to express wild-type and bm mutant F-MLV Gag-GFP/Env-mCherry. One day later, cells were fixed, incubated with Alexa Fluor 647-conjugated anti-mCherry antibody, and examined by epifluorescence microscopy. The GFP and mCherry signals represent the total Gag and total Env, respectively. The Alexa Fluor 647 signal represents the surface-exposed Env. (B) An experiment as in panel A was performed with primary B cells. Single Z-planes are displayed. Scale bar, 10 μm.