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Mol. Cell. Biol., Oct 1995, 5777-5788, Vol 15, No. 10
CY Chen, N Xu and AB Shyu
Poly(A) tail removal is a critical first step in the decay pathway for many
yeast and mammalian mRNAs. Poly(A) shortening rates can be regulated by
cis-acting sequences within the transcribed portion of mRNA, which in turn
control mRNA turnover rates. The AU-rich element (ARE), found in the 3'
untranslated regions of many highly labile mammalian mRNAs, is a
well-established example of this type of control. It represents the most
widespread RNA stability determinant among those characterized in mammalian
cells. Here, we report that two structurally different AREs, the c-fos ARE
and the granulocyte-macrophage colony- stimulating factor (GM-CSF) ARE,
both direct rapid deadenylation as the first step in mRNA degradation, but
by different kinetics. For c-fos- ARE-mediated decay, the mRNA population
undergoes synchronous poly(A) shortening and is deadenylated at the same
rate, implying the action of distributive or nonprocessive ribonucleolytic
digestion of poly(A) tails. In contrast, the population of
granulocyte-macrophage colony- stimulating factor ARE-containing mRNAs is
deadenylated asynchronously, with the formation of fully deadenylated
intermediates, consistent with the action of processive ribonucleolytic
digestion of poly(A) tails. An important general implication of this
finding is that different RNA- destabilizing elements direct deadenylation
either by modulating the processivity at which a single RNase functions or
by recruiting kinetically distinct RNases. We have also employed targeted
inhibition of translation initiation to demonstrate that the
RNA-destabilizing function of both AREs can be uncoupled from translation
by ribosomes. In addition, a blockade of ongoing transcription has been
used to further probe the functional similarities and distinctions of these
two AREs. Our data suggest that the two AREs are targets of two distinct
mRNA decay pathways. A general model for ARE-mediated mRNA degradation
involving a potential role for certain heterogeneous nuclear
ribonucleoproteins and ARE-binding proteins is proposed.
Copyright © 1995, American Society for Microbiology
mRNA decay mediated by two distinct AU-rich elements from c-fos and granulocyte-macrophage colony-stimulating factor transcripts: different deadenylation kinetics and uncoupling from translation
Department of Biochemistry and Molecular Biology, Medical School, University of Texas Houston Health Science Center 77030, USA.
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