Phospholipid transfer activity is relevant to but not sufficient for the essential function of the yeast SEC14 gene product.
To investigate several key aspects of phosphatidylinositol transfer protein (PI-TP) function in eukaryotic cells, rat PI-TP was expressed in yeast strains carrying lesions in SEC14, the structural gene for yeast PI-TP (SEC14p), whose activity is essential for Golgi secretory function in vivo. Rat PI-TP expression effected a specific complementation of sec14ts growth and secretory defects. Complementation of sec14 mutations 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 associate with yeast Golgi membranes and was not a result of rat PI-TP stabilizing the endogenous sec14ts gene product. These collective data demonstrate that while the in vitro PI-TP activity of SEC14p clearly reflects some functional in vivo property of SEC14p, the PI-TP activity is not the sole essential activity of SEC14p. Those data further identify an efficient Golgi targeting capability as a likely essential feature of SEC14p function in vivo. Finally, the data suggest that stable association of SEC14p with yeast Golgi membranes is not a simple function 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 indicate that a mammalian PI-TP can stimulate Golgi secretory function in vivo.
Skinner
H B
HB
Department of Cell Biology, University of Alabama at Birmingham 35294-0005.
Alb
J G
JG
Whitters
E A
EA
Helmkamp
G M
GM
Bankaitis
V A
VA
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D004274:DNA, Recombinant; D005455:Fluorescent Antibody Technique; D005800:Genes, Fungal; D005816:Genetic Complementation Test; D006056:Golgi Apparatus / Q000378:metabolism; D015151:Immunoblotting; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins
D002352:Carrier Proteins; D004274:DNA, Recombinant; D008565:Membrane Proteins; D010716:Phosphatidylinositols; D049294:Phospholipid Transfer Proteins; C483438:SEC14 protein, S cerevisiae; C118289:SEC24 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins