Figure 5.

Pulse-chase analysis of class II transport through distinct subcellular organelles. Cells were labeled for 20 min with [³⁵S-]methionine/cysteine, followed by a chase for the times indicated in the absence of radiolabel. At each time point, cells were homogenized and membranes fractionated by sucrose density centrifugation followed by organelle electrophoresis as described in Fig. 2. Shifted (lanes 1 and 3) and unshifted (lanes 2 and 4) membranes were pooled, class II molecules immunoprecipitated and analyzed by SDS-PAGE and fluorography.