Cargo in Golgi elements forms large domains rapidly by lateral segregation Transiently expressed VSVG3-YFP cargo was accumulated in the ER and pulsed into the secretory pathway of PtK2 cells as in Figure 1B. Time at 32°C and the frame number from the movie in Additional Fileset 3 are indicated. Cargo and Golgi resident initially coincide in Golgi elements, with small domains of cargo visible (47:15). Within 11 s, a large region containing primarily cargo pulls off (47:35, arrowhead 1) and by 49:18 consolidates into a more compact cargo domain. This domain retains a core of membrane containing T2-CFP. A smaller cargo domain pulls off beginning at 47:16 (arrowhead 2), and an additional large domain coalesces rapidly between 49:18 and 52:22 (arrowhead 3). Cargo domains and Golgi elements exhibit complementary dynamics (Results), indicating they are regions of a contiguous structure. Bar: 5 μm.