The Full Complement of Yeast Ypt/Rab-GTPases and Their Involvement in Exo- and Endocytic Trafficking - Fusion of Biological Membranes and Related Problems - page 160

FIGURE 3. Vesicular protein transport pathways and known sites of action of Ypt GTPases
(white symbols) and yeast syntaxins (black symbols). Filled arrows indicate forward transport
while open arrows indicate retrograde trafficking. Ypt GTPases and syntaxins involved in
secretion are essential proteins, whereas loss of the endocytic Ypt proteins or all syntaxins of
the endocytic/VPS pathway (Holthuis et al., 1998b) does not result in lethality. e.E. = early
endosome, I.E. = late endosome, Plm = plasma membrane.
ascribed to the t-SNARE Tlg2p (Holthuis et al., 1998a), however, this
protein might also be involved in endosome biogenesis (Seron et al., 1998).
In both cases, interpretation of the data is complicated by the rather subtle
phenotype of the tlg2 gene disruption. Docking to the prevacuolar com-
partment is regulated by Ypt51p and might in addition be influenced by the
other members of the Ypt5p sub-family. The syntaxin-like Pep12-protein
has been shown to act at the same transport step (Becherer et al., 1996).
Vesicle docking and fusion at the vacuole are mediated by Ypt7p and
Vam3p, respectively (Nichols et al., 1997). The observation that, upon high
expression, Pep12p and Vam3p can functionally replace each other is
most likely due to a saturation of the sorting machinery under these