Ultracentrifugation-based approaches to study regulation of Sec6/8 (exocyst) complex function during development of epithelial cell polarity.

The Sec6/8 (exocyst) complex is an essential component of the exocytic apparatus and plays an evolutionarily conserved role in polarized membrane growth. During development of epithelial cell polarity, this cytosolic protein complex is recruited to plasma membrane sites of cell-cell contact, where it facilitates exocytosis to the lateral membrane domain. However, the identity of membrane binding sites for Sec6/8 complex, mechanisms regulating association of Sec6/8 complex with these sites, and the precise function of the complex in polarized trafficking are not known. Biochemical strategies involving differential, rate-zonal, and isopycnic density gradient ultracentrifugation are providing clues to these questions.