Fig. 1. Immuno-EM shows that EGFR is localized mainly outside caveolae. Ultrathin cryosections of nonstimulated cells were double labeled to localize EGFR (large gold particles) and caveolin (small gold particles). A431 cells (A,B) showed strong labeling for EGFR but very limited colocalization of EGFR (large arrowheads) with caveolin in caveolae. In HEp-2 cells (C,D) EGFR labeling was less intense but, as in A431 cells, EGFR labeling was mainly at smooth noninvaginated areas of the plasma membrane (small arrowheads) with only small amounts colocalizing (large arrowheads) with caveolin in caveolae. Bars, 100 nm.