Molecular Biology

When the Party's Over

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Science  25 Aug 2000:
Vol. 289, Issue 5483, pp. 1259
DOI: 10.1126/science.289.5483.1259b

Eukaryotic messenger RNAs (mRNAs) carry at their 3' ends a tail of approximately 250 adenylate residues that are added by a template-independent nucleotidyl transferase known as poly(A) polymerase; crystal structures of the mammalian (Martin et al.) and yeast (Bard et al., Reports, this issue, p. 1346) enzymes have been solved. These poly(A)+ mRNAs are transported from the nucleus to the cytoplasm and protected from degradation while they await translation by the ribosome. One implication is that when the time for disposal arrives, there must be a safeguard to ensure that partially degraded or poly(A) mRNAs are not translated.

Searfoss and Wickner report results indicating that in yeast the putative RNA helicase Ski2p contributes to disfavoring translation of nonadenylated RNAs and that the translation apparatus is intrinsically able to operate on poly(A)-deficient mRNAs. Previous work had shown the involvement of Ski2p in a multiprotein complex—the exosome—which incorporates several 3' to 5' exoribonuclease activities. Thus, there appear to be several mechanisms that together serve to shunt the translational apparatus away from messages earmarked for recycling. — GJC

EMBO J.19, 4193 (2000); Proc. Natl. Acad. Sci. U.S.A.97, 9133 (2000).

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