The liquid crystallinity of spider dragline silk dope is thought to be impo
rtant for both the spinning process and the extreme mechanical properties o
f the final thread. Although the formation of the liquid crystalline units
is poorly understood, it has been suggested that spider silk proteins are s
ecreted in a random coil and then aggregate end-to-end into rod-shaped unit
s to form supramolecular liquid crystals. However, evidence presented here
from transmission electron microscopy indicates that coat protein of the dr
agline silk of a Nephila spider is stored as hexagonal columnar liquid crys
tals within the intracellular secretory vesicles. This implies that this. c
omponent is already folded into short rods within the gland cells and forms
molecular rather than supramolecular liquid crystals, (C) 1999 Harcourt Pu
blishers Ltd.