  The yeast Saccharomyces cerevisiae is one of the best characterized
eukaryotic models. The secretory pathway was the first trafficking pathway
clearly understood mainly thanks to the work done in the laboratory of Randy
Schekman in the 1980s. They have isolated yeast sec mutants unable to secrete
an extracellular enzyme and these SEC genes were identified as encoding key
effectors of the secretory machinery. For this work, the 2013 Nobel Prize in
Physiology and Medicine has been awarded to Randy Schekman; the prize is shared
with James Rothman and Thomas S{\"u}dhof. Here, we present the different
trafficking pathways of yeast S. cerevisiae. At the Golgi apparatus newly
synthesized proteins are sorted between those transported to the plasma
membrane (PM), or the external medium, via the exocytosis or secretory pathway
(SEC), and those targeted to the vacuole either through endosomes (vacuolar
protein sorting or VPS pathway) or directly (alkaline phosphatase or ALP
pathway). Plasma membrane proteins can be internalized by endocytosis (END) and
transported to endosomes where they are sorted between those targeted for
vacuolar degradation and those redirected to the Golgi (recycling or RCY
pathway). Studies in yeast S. cerevisiae allowed the identification of most of
the known effectors, protein complexes, and trafficking pathways in eukaryotic
cells, and most of them are conserved among eukaryotes.
