But whereas some isolated proteins can be dena- 
tured and refolded in vitro in the absence of other 
macromolecular cellular components, folding and 
assembly of polypeptides in vivo involves other 
proteins, many of which belong to families that have 
been highly conserved during evolution. These pro- 
teins, known as chaperones, are involved at all 
stages of cellular metabolism: during protein synthe- 
sis, membrane translocation, and folding; in re- 
arrangements of macromolecules during functional 
cycles of assembly and disassembly; in protection 
from environmental stress; and in targeting proteins 
for degradation. 
ER chaperone BiP provides an ideal system to 
study in detail the interactions between one chaper- 
one and its substrates. BiP binds transiently to newly 
synthesized wild-type polypeptides and more per- 
manently to malfolded or unassembled proteins. 
Under normal growth conditions BiP is synthesized 
constitutively and abundantly, comprising ~5% of 
the luminal content of the ER. However, its synthe- 
sis can be further induced by the accumulation of 
mutant proteins in the ER or by a variety of stress 
conditions whose common denominator is likely to 
be the generation in the ER of misfolded polypep- 
tides. The overall goals of this investigation are 1) to 
determine how BiP discriminates between folded 
and unfolded structures and what role it plays dur- 
ing protein folding and 2) to elucidate the pathway 
of induction of the BiP gene in response to the accu- 
mulation of unfolded proteins. Three experimental 
systems are being utilized: mammalian cells for anal- 
ysis of in vivo interactions between BiP and its pro- 
tein substrates, Escherichia coli for expression of 
BiP proteins and of peptide libraries for in vitro 
binding studies, and the yeast Saccharomyces cere- 
visiae for genetic analysis of the pathway of induc- 
tion of BiP synthesis. 
Dr. Gething is also Professor of Biochemistry at 
the University of Texas Southwestern Medical 
Center at Dallas. 
Articles 
Bassel-Duby, R., Jiang, N.-Y., Bittick, T., Ma 
dison, E., McGookey, D., Orth, K., Shohet, R., 
Sambrook, J. P., and Gething, M.-J. 1992. Tyro- 
sine 67 in the epidermal growth factor-like do- 
main of tissue-type plasminogen activator is im- 
portant for clearance by a specific hepatic 
receptor. /j5/o/ Chem 267:9668-9677. 
Gething, M.-J. 1991. Molecular chaperones: indi- 
vidualists or groupies? Curr Opin Cell Biol 
3:610-614. 
Gething, M.-J., and Sambrook,]. 1992. Proteinfold- 
ing in the cell. Nature 355:33-45. 
Mori, K., Sant, A., Kohno, K., Normington, K., 
Gething, M.-J. , and Sambrook ,J.E.1992.A22bp 
c?5-acting element is necessary and sufficient for 
the induction of the yeast KAR2 (BiP) gene by 
unfolded proteins. EMBO f 1 1 :2583-2593. 
Orth, K., Madison, E.L., Gething, M.-J., Sambrook, 
J.F., and Herz, J. 1992. Complexes of tissue-type 
plasminogen activator and its serpin inhibitor 
plasminogen-activator inhibitor type 1 are inter- 
nalized by means of the low density lipoprotein 
receptor-related protein/a2-macroglobulin re- 
ceptor. Proc Natl Acad Sci USA 89:7422-7426. 
Segal, M.S., Bye, J.M., Sambrook, J. F., and Gething, 
M.-J. 1992. Disulfide bond formation during the 
folding of influenza virus hemagglutinin. / Cell 
Biol 118:227-244. 
MEMBRANE LIPIDS AND THE REGULATION OF CELL FUNCTION 
John A. Glomset, M.D., Investigator 
Current research in Dr. Glomset's laboratory is 
focused on the lipids of animal cells. In one set of 
studies, structural determinants that affect the inter- 
actions of phosphorus-containing lipids in cell 
membranes are being examined at a molecular 
level . A recently completed, computer-based molec- 
ular modeling study of the efi'ects of phospholipid 
polyunsaturated fatty acids on these interactions led 
to three major findings: 1) the presence of multiple 
cis double bonds in a polyunsaturated fatty acid 
chain need not prevent that chain from adopting a 
straight conformation; 2) the presence of an esteri- 
fied, polyunsaturated fatty acyl chain in a lipid need 
not interfere with that lipid's ability to pack with 
similar lipids in tightly packed monolayers; and 3) 
the precise packing geometry of polyunsaturated 
lipid molecules in a monolayer can be a function of 
the location of the sequence of cis double bonds 
within the polyunsaturated fatty acyl chain. To- 
gether these findings provide important clues 
concerning factors that may influence the do- 
main structure of animal cell membranes. There- 
fore, experimental tests of the models with well- 
characterized phospholipids are under way, in 
CELL BIOLOGY AND REGULATION 6 1 
