Ultrastructural localization of full-length polycystin-2 and polycystin-2 (1–703). COS-7 cells were transiently transfected with expression plasmids for full-length polycystin-2 (a) and polycystin-2 (1–703) (b and c) fused with EGFP and the tetracysteine motif. (a and b) Cells with EGFP fluorescence. Asterisks in b indicate Golgi cisternae with an osmiophilic diaminobenzidine precipitate in a cell producing the truncated polycystin-2 protein. No such precipitate can be seen in a cell producing full-length polycystin-2. (c) A cell without EGFP fluorescence served to demonstrate background staining. The arrows in a and c point to clathrin-coated budding vesicles marking the trans-Golgi network. Bar, 200 nm.