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Mol. Cell. Biol., 04 1995, 2219-2230, Vol 15, No. 4
AM Zubiaga, JG Belasco and ME Greenberg
Labile mRNAs that encode cytokine and immediate-early gene products often
contain AU-rich sequences within their 3' untranslated region (UTR). These
AU-rich sequences appear to be key determinants of the short half-lives of
these mRNAs, although the sequence features of these elements and the
mechanism by which they target mRNAs for rapid decay have not been fully
defined. We have examined the features of AU- rich elements (AREs) that are
crucial for their function as determinants of mRNA instability in mammalian
cells by testing the ability of various mutant c-fos AREs and synthetic
AREs to direct rapid mRNA deadenylation and decay when inserted within the
3' UTR of the normally stable beta-globin mRNA. Evidence is presented that
the pentamer AUUUA, which previously was suggested to be the minimal
determinant of instability present in mammalian AREs, cannot direct rapid
mRNA deadenylation and decay. Instead, the nonomer UUAUUUAUU is the
elemental AU-rich sequence motif that destabilizes mRNA. Removal of one
uridine residue from either end of the nonamer (UUAUUUAU or UAUUUAUU)
results in a decrease of potency of the element, while removal of a uridine
residue from both ends of the nonamer (UAUUUAU) eliminates detectable
destabilizing activity. The inclusion of an additional uridine residue at
both ends of the nonamer (UUUAUUUAUUU) does not further increase the
efficacy of the element. Taken together, these findings suggest that the
nonamer UUAUUUAUU is the minimal AU- rich motif that effectively
destabilizes mRNA. Additional ARE potency is achieved by combining multiple
copies of this nonamer in a single mRNA 3' UTR. Furthermore, analysis of
poly(A) shortening rates for ARE- containing mRNAs reveals that the
UUAUUUAUU sequence also accelerates mRNA deadenylation and suggests that
the UUAUUUAUU motif targets mRNA for rapid deadenylation as an early step
in the mRNA decay process.
Copyright © 1995, American Society for Microbiology
The nonamer UUAUUUAUU is the key AU-rich sequence motif that mediates mRNA degradation
Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115.
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