ABSTRACT
Eukaryotic cells rely for their viability on the partitioning of many basic cellular processes into membrane-bounded organelles. These are the nucleus, endoplasmic reticulum (ER), Golgi apparatus, endosomes, vacuolar compartment, mitochondria and peroxisomes (Figure 7.1). Most molecules destined for the vacuole, cell surface and outside the cell are routed through the ER and Golgi, which, together with the vesicular intermediates between them, comprise the secretory pathway (Palade, 1975). The targeting and trafficking problems posed by this complex organization have been the subject of intense study in yeast and other systems. Proteins must be recognized as destined for partitioning outside the cytosol, targeted to and then translocated across the correct membrane. In the early secretory pathway compartments – the ER and Golgi – proteins are sorted, modified and often assembled into complexes en route to their final destination. Incorrectly assembled proteins are retained in the ER until they fold correctly or are targeted for degradation.
