Molecular Biology and Evolution, Vol 14, 1050-1061, Copyright © 1997 by Society for Molecular Biology and Evolution
CE Norris, MA Brown, E Hickey, LA Weber and LE Hightower
The heat shock response of a fish which inhabits a highly stressful
environment (Poeciliopsis lucida, a minnow from river systems of the
Sonoran desert in northwestern Mexico) was investigated. Cells derived from
this fish exhibited a typical heat shock response when exposed to elevated
temperature, synthesizing high levels of 90 kDa, 70 kDa, and 30 kDa heat
shock proteins (Hsp90, Hsp70, and Hsp30), as well as lower amounts of other
heat shock proteins. Additional small heat shock proteins (sHSPs),
including Hsp27, were induced after a prolonged heat shock at a time when
synthesis of Hsp70 and Hsp30 was decreasing. Characterization of cDNA
clones for hsp27 and hsp30 revealed that both are members of the
alpha-crystallin/sHSP superfamily but belong to separate lineages within
this gene family. The multiple isoforms of P. lucida Hsp30 appear to be
members of a multigene family and are most closely related to salmon and
Xenopus Hsp30s. In contrast, Hsp27 is highly similar to mammalian and avian
sHSPs; it was synthesized as three isoforms which represented
differentially phosphorylated forms of a single polypeptide. In
Poeciliopsis, the various sHSPs may each perform a subset of the roles
attributed to mammalian sHSPs. The conservation of phosphorylation sites in
Hsp27 may indicate an involvement in signal transduction to the actin
cytoskeleton. The hsp30 genes appear to have diverged more rapidly than the
corresponding hsp27 genes; the various members of the Hsp30 family may
function as molecular chaperones and, in this role, may be less
evolutionarily constrained. Finally, the presence of these two classes of
sHSP in a single taxon indicates that these two lineages arose by gene
duplication early in the evolution of vertebrates and raises questions
about the fate of homologs of Hsp30 in mammals and of Hsp27 in Xenopus.
ORIGINAL ARTICLE
Low-molecular-weight heat shock proteins in a desert fish (Poeciliopsis lucida): homologs of human Hsp27 and Xenopus Hsp30
Department of Molecular and Cell Biology, University of Connecticut, Storrs 06269-3044, USA.
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