PLANT PHYSIOLOGY , Vol 114, Issue 4 1477-1485, Copyright © 1997 by American Society of Plant Biologists
|
WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Expression and Native Structure of Cytosolic Class II Small Heat-Shock Proteins
K. W. Helm, G. J. Lee and E. Vierling
Department of Biology, Siena College, Loudonville, New York 12211 (K.W.H.)
Higher plants synthesize small heat-shock proteins (smHSPs) from five
related gene families. The class I and II families encode cytosolic smHSPs.
We characterized the class II smHSPs of pea (Pisum sativum) and compared
them with class I smHSPs. Antibodies against recombinant HSP17.7, a class
II smHSP, recognized four heat-inducible 17- to 18-kD polypeptides and did
not cross-react with class I smHSPs. On sucrose gradients the class II
smHSPs sedimented primarily at 8 Svedberg units, indicating that they are
components of large complexes similar in size to class I smHSP complexes.
However, the class I and II complexes were readily distinguishable by
nondenaturing polyacrylamide gel electrophoresis and isoelectric focusing.
Nondenaturing immune precipitations using anti-HSP17.7 or anti-HSP18.1 (a
class I smHSP) antiserum provide further evidence that the class I and II
smHSPs exist in different complexes, composed primarily of smHSPs.
Recombinant HSP17.7 and HSP18.1 formed complexes of sizes similar to those
formed in vivo. When these two smHSPs were mixed, denatured with urea, and
then dialyzed, the distinct class I and II complexes again formed, each
containing only HSP18.1 or HSP17.7. Thus, cytosolic smHSPs from two related
gene families expressed simultaneously form distinct complexes in vivo,
suggesting that they have subtly different functions.
