The Signal Sequence Coding Region Promotes Nuclear Export Of MRNA

Main Category: Biology / Biochemistry
Article Date: 03 Dec 2007 - 17:00 PDT

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In eukaryotic cells, precursors of messenger RNAs (mRNAs) are synthesized and processed in the nucleus. The noncoding introns are spliced out, and a cap and poly-adenosine sequence are added to the beginning and end of the transcript, respectively. The resulting mature mRNA is exported from the nucleus to the cytoplasm by crossing the nuclear pore. Both the introns and the cap help to recruit factors that are necessary for nuclear export of an mRNA. In a new study published this week in the open-access journal PLoS Biology, Alexander Palazzo, Tom Rapoport, and colleagues provide evidence for a novel mRNA export pathway that is specific for transcripts coding for secretory proteins. These proteins contain signal sequences that target them for translocation across the endoplasmic reticulum membrane.

The researchers made the surprising observation that the signal sequence coding region (SSCR) can serve as a nuclear export signal of an mRNA that lacks an intron or functional cap. Even the export of an intron-containing natural mRNA was enhanced by its SSCR. The SSCR export signal appears to be characterized in vertebrates by a low content of adenines. Their discovery of an SSCR-mediated pathway explains the previously noted amino acid bias in signal sequences, and suggests a link between nuclear export and membrane targeting of mRNAs.

Citation: Palazzo AF, Springer M, Shibata Y, Lee CS, Dias AP, et al. (2007) The signal sequence coding region promotes nuclear export of mRNA. PLoS Biol 5(12): e322. doi:10.1371/journal.pbio.0050322
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