J. Biol. Chem., Vol. 265, Issue 24, 14156-14162, Aug, 1990
Ferritin is a translationally regulated heat shock protein of avian reticulocytes
BG Atkinson, TW Blaker, J Tomlinson and RL Dean
Department of Zoology, University of Western Ontario, London, Canada.
Heat-shock avian reticulocytes exhibit enhanced synthesis of a greater than
450-kDa protein. Biochemical, immunochemical, and visual criteria were used
to identify this protein as the iron storage protein ferritin. The 21-kDa
ferritin subunits synthesized during heat shock are similar in size and pI
to the subunits that are constitutively synthesized. The 2-6-fold heat
shock-induced increase in ferritin synthesis appears to be regulated at the
translational level as it is insensitive to actinomycin D. Northern and
dot-blot hybridization analyses of cytoplasmic RNAs with avian H-ferritin
cDNA fragments support the contention that the heat shock stimulation of
ferritin synthesis is translationally regulated. These latter studies
demonstrate that the heat shock-induced synthesis of ferritin does not
involve a change in the amount of total cytoplasmic ferritin mRNAs, but
rather appears to entail a translocation of cytoplasmic H-ferritin mRNAs
from a polyribosome-free, translationally repressed state to a
polyribosome-associated, translationally active state. These results
suggest that thermally stressed avian reticulocytes have a critical and
functional need for the synthesis of additional ferritin and that its
enhanced synthesis, unlike the new and/or enhanced synthesis of the
well-established avian heat shock proteins, is regulated wholly at the
translational level.
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