MOLECULAR BIOLOGY: Surveillance by No-bodies

Science  21 Apr 2006:
Vol. 312, Issue 5772, pp. 338c
DOI: 10.1126/science.312.5772.338c

Within eukaryotic cells, mRNAs that contain errors are subject to strict quality-control measures and are rapidly degraded to prevent any inadvertent molecular catastrophes. Dez et al. reveal some of the nuts and bolts of a similar quality-control system that monitors ribosome biogenesis. Ribosomes are built in the nucleolus and nucleoplasm before being exported into the cytoplasm, where they undergo final maturation and function as the protein-synthesizing workhorses of the cell. Dez et al. find that preventing the export of “under-construction” pre-ribosomes results in the rapid appearance of ribosomal RNA (rRNA) and protein components in distinct nucleolar foci they christen “No-bodies.” Components of the nuclear exosome and the TRAMP polyadenylation complex—molecular assemblies that have been implicated in the elimination of defective nuclear RNAs—are also found to accumulate in the No-body, and furthermore, they seem to be responsible for concentrating the pre-60S ribosomes here. The large rRNAs are polyadenylated within the subcellular foci by the TRAMP complex, and this mark seems to tag the rRNAs for destruction by the exosome. Based on these results, the authors suggest that the No-body is the site at which surveillance of pre-ribosomes occurs, and they speculate that defects in maturation might be identified by the failure to displace pre-ribosome-associated factors, resulting in the recruiting of TRAMP. — GR

EMBO J. 25, 1534 (2006).

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