MOLECULAR BIOLOGY: Remembering the First Time

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Science  21 Sep 2001:
Vol. 293, Issue 5538, pp. 2173b
DOI: 10.1126/science.293.5538.2173b

Translation, or the making of proteins from messenger RNA (mRNA), relies on the exact registration of codons (three consecutive nucleotides). A shift in reading frame can result in a termination codon being created from the joining of parts of two codons. Such a deleterious junction can also result from inexact splicing, which is the process that removes intervening sequences from the pre-mRNA. Recent work suggests that when the ribosome transits the mRNA for the first time, a quality control mechanism checks to see if the termination codon lies downstream of all of the exon-exon junctions. If not, then components of the nonsense-mediated decay (NMD) machinery may be recruited by the junctional complexes (as described by Le Hir et al. and by Kim et al. and Lykke-Andersen et al., 7 Sept., Reports, pp. 1832 and 1836).

Ishigaki et al. show that two cap-binding proteins, CBP80 and CBP20, bind to the 5′ end of the mRNA in the nucleus and are then replaced by the mainly cytoplasmic eukaryotic initiation factor 4E. This swap may provide the signal (perhaps one of many) that no premature termination codons are present and that the likelihood of synthesizing a truncated protein (which may have a dominant negative function) is small. — GJC

EMBO J. 20, 4987 (2001); Cell 106, 607 (2001).

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