Volume 272, Number 11,
Issue of March 14, 1997
pp. 7306-7313
©1997 by The American Society for Biochemistry and Molecular Biology, Inc.
Heat Shock Inhibits Release of the Signal Recognition
Particle from the Endoplasmic Reticulum in Barley Aleurone
Layers
(Received for publication, September 23, 1996, and in revised form, January 7, 1997)
Boyang
Chu
,
Mark R.
Brodl
§
and
Faith C.
Belanger
From the
Dana Farber Cancer Institute,
Boston, Massachusetts 02115, the § Department of
Biology, Knox College, Galesburg, Illinois 61401, and the Center
for Agricultural Molecular Biology, Rutgers University,
New Brunswick, New Jersey 08903
When barley (Hordeum vulgare)
aleurone layers are subjected to heat shock there is a selective
degradation of the normally stable mRNAs encoding secreted
proteins. Messages for nonsecreted proteins are not degraded. The
synthesis of heat shock proteins is not required for this selective
message degradation. Our hypothesis explaining this phenomenon is that
a component of the early steps in the synthesis of secreted proteins is
damaged by heat shock, resulting in a selective halt in translation on
secretory mRNAs, which may in turn lead to degradation of those
messages. The first committed step in the synthesis of secreted
proteins is the binding of the nascent signal sequence to the signal
recognition particle. We have obtained cDNA clones and antibodies
for the barley 54-kDa subunit of the signal recognition particle. In
cell fractionation experiments, more signal recognition particle was
bound to the endoplasmic reticulum membranes and less was in the free
particle fraction following a heat shock. The results suggest that heat shock inhibits the release of the signal recognition particle from the
endoplasmic reticulum. This would, in turn, inhibit the resumption of
translation and may be the underlying cause of the secretory message
degradation.