FIG 7.

Immunoelectron micrographs of MHR mutants arrested as assembly intermediates at the PM. COS-1 cells infected with proviruses expressing WT Gag or the indicated mutants were analyzed by double-label immuno-EM, using antibodies to Gag and ABCE1. Small gold particles indicate Gag labeling; large gold particles indicate ABCE1 labeling. Images were chosen from the quantitative immuno-EM experiments (Fig. 8 and Table 1) and represent the approximate distribution of targeted Gag, early assembly, and late assembly sites at the PM observed for each group. Dark arrows show Gag clusters at the PM that are colocalized with ABCE1; white arrowheads show Gag clusters at the PM that are not colocalized with ABCE1. Dashed lines are placed in some locations to help viewers identify the PM. Bars, 200 nm. As described previously (30), not all instances of colocalization are captured by immuno-EM since the 50-nm sections capture only a fraction of the ∼100-nm-diameter capsid. Targeted Gag, early assembly sites, and late assembly sites are defined in the text and in Table 1.