REDRAWING COMPARTMENTAL BOUNDARIES IN THE EXOCYTIC PATHWAY

Compartments can be defined both morphologically as well as biochemica lly. The former relies on a direct visualisation of membrane boundarie s and the latter by the characterisation of enzymatic functions taking place within the compartment. The combination of morphology and bioch emistry has led to the identification of several compartments within t he exocytic pathway, each assumed to carry out independent functions i n a logical succession [Palade, G. (1975) Science 189, 347-358]. Howev er, recent findings show that resident enzymes are confined to not one but at least two adjacent compartments suggesting that morphological and biochemical definitions do not coincide. We will here discuss thes e findings and propose a model to explain how compartments are organis ed and maintained along the exocytic pathway.