I. Introduction THE transport of proteins, hormones, and nutrients to different locations within a cell is an essential process for many of the functions of eukaryotic cells. It is of particular importance in complex multicellular organisms to enable the cells to communicate with one another. The pathways for transport of materials into and out of cells utilize a variety of large membrane compartments within the cell, which communicate with each other and with the external environment via smaller membrane carriers called transport vesicles, The movement of the transport vesicles between compartments or to the plasma membrane is called membrane or vesicle trafficking. This is a highly ordered and directed process and takes a variety of different forms that are unique for a particular cellular function. Like intercellular communication, intracellular transport pathways are multidirectional in nature, primarily being composed of trafficking between intracellular structures, the exocytptic (secretory) pathway...