Cellular traffic and markers of subcellular compartments

Cellular membranes play very important roles. They not only constitute envelopes that enclose the cytoplasm and the organelles, but they also are dynamic structures that are in a constant state of turnover, with their own substance being continuously shuffled, redistributed and renewed. These processes of intracellular. membranes, in various compartments, relate essentially, to cell traffic. Since the early work of George Palade's and Christian de Duve's groups, in which the relationship between transporting vesicles and distinct separate subcellular compartments was shown, many new facts and concepts were brought about by the use of refined techniques of immunocytochemistry, the set up of cell free systems for the reconstitution of intracellular transport and the study of secretion mutants in yeast. In more recent years, the field was considerably extended by the emergence of the G-proteins. Now, we begin to comprehend that members of various gene families of GTP-GDP binding proteins play important parts in vesicle coating, transport and targetting in the endocytic and exocytic secretory pathways: trimeric G-proteins, dynamins, ARF (ADP-ribosylating factors) and RAS-related proteins. Among all these, members of the Rab subfamily, which appear to exert identical functions in different locations, might be considered as dynamic and specific markers of subcellular compartments.