Two roles of the cellular chaperone protein GRP78-BiP in the endoplasmic 
reticulum (ER). This protein, a member of the stress (heat-shock) family, is 
a resident component of the ER and has peptide- binding activity. The top 
section illustrates the specific and transient association of GRP78-BiP (dot- 
ted oval) with a viral glycoprotein, hemagglutinin- neuraminidase, during 
its synthesis and folding in the ER. These entities provide an interesting 
model system, as GRP78-BiP is known to be released from the glycoprotein 
at a point in time prior to oligomerization. The bottom section illustrates the 
more stable association of GRP78-BiP with malfolded integral membrane 
proteins in the ER. If the protein contains a lesion that prevents native fold- 
ing, then GRP78-BiP remains associated with it and normal oligomeriza- 
tion does not occur. 
Research of Robert A. Lamb. 
