Regulation of intracellular membrane transport.

A number of proteins that are necessary for membrane transport have been identified using cell-free assays and yeast genetics. Although our knowledge of transport mechanisms remains limited, common themes are clearly emerging. In particular, specific GTP-binding proteins appear to be involved, not only at all steps of membrane traffic but also at more than one check-point within each step. The ordered sequence of events occurring during vesicle formation, targeting and fusion may be regulated in a stepwise manner by specific GTP-dependent switches, which act as modular elements of the transport mechanism.