Hb. Skinner et al., PHOSPHOLIPID TRANSFER ACTIVITY IS RELEVANT TO BUT NOT SUFFICIENT FOR THE ESSENTIAL FUNCTION OF THE YEAST SEC14 GENE-PRODUCT, EMBO journal, 12(12), 1993, pp. 4775-4784
To investigate several key aspects of phosphatidylinositol transfer pr
otein (PI-TP) function in eukaryotic cells, rat PI-TP was expressed in
yeast strains carrying lesions in SEC14, the structural gene for yeas
t PI-TP (SEC14p), whose activity is essential for Golgi secretory func
tion in vivo. Rat PI-TP expression effected a specific complementation
of sec14ts growth and secretory defects. Complementation of sec14 mut
ations was not absolute as rat PI-TP expression failed to rescue sec14
null mutations. This partial complementation of sec14 lesions by rat
PI-TP correlated with inability of the mammalian protein to stably ass
ociate with yeast Golgi membranes and was not a result of rat PI-TP st
abilizing the endogenous sec14ts gene product. These collective data d
emonstrate that while the in vitro PI-TP activity of SEC14p clearly re
flects some functional in vivo property of SEC14p, the PI-TP activity
is not the sole essential activity of SEC14p. Those data further ident
ify an efficient Golgi targeting capability as a likely essential feat
ure of SEC14p function in vivo. Finally, the data suggest that stable
association of SEC14p with yeast Golgi membranes is not a simple funct
ion of its lipid-binding properties, indicate that the amino-terminal
129 SEC14p residues are sufficient to direct a catalytically inactive
form of rat PI-TP to the Golgi and provide the first evidence to indic
ate that a mammalian PI-TP can stimulate Golgi secretory function in v
ivo.