Fig. 4. COS7 cells transfected for ßPIX-HA (A,B) or GIT1-Flag (C,D). (A,B) Double immunogold labelling on ultrathin cryosections. ßPIX-HA (gold, 15 nm), identified by antibodies to HA, labels extensively large intracellular structures. ßPIX-HA (gold, 15 nm) and endogenous TfR (gold, 10 nm) scarcely colocalize within these structures (arrows in B). (C) Immunogold labelling of ultrathin cryosection for GIT1 (gold, 15 nm), identified by antibodies to Flag. GIT1 labels extensively large intracellular structures and endosomes (arrow). (D) Transferrin receptor (TfR, gold 10 nm) associates with similar electron dense structures. Bars, (A) 470 nm; (B) 180 nm; (C) 140 nm; (D) 57 nm.