Mrna sequence code#

Even the export of an intron-containing natural mRNA was enhanced by its SSCR. We 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. These proteins contain signal sequences that target them for translocation across the endoplasmic reticulum membrane. Here we provide evidence for a novel mRNA export pathway that is specific for transcripts coding for secretory proteins. Both the introns and the cap help to recruit factors that are necessary for nuclear export of an mRNA.

The resulting mature mRNA is exported from the nucleus to the cytoplasm by crossing the nuclear pore. During processing, noncoding introns are spliced out, and a cap and poly-adenosine sequence are added to the beginning and end of the transcript, respectively. In eukaryotic cells, precursors of messenger RNAs (mRNAs) are synthesized and processed in the nucleus. The 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.

The SSCR export signal appears to be characterized in vertebrates by a low content of adenines, as demonstrated by genome-wide sequence analysis and by the inhibitory effect of silent adenine mutations in SSCRs. Like conventional export, the SSCR-dependent pathway required the factor TAP, but depletion of the TREX components had only moderate effects. The mRNAs were injected into the nucleus or synthesized from injected or transfected DNA, and their export was followed by fluorescent in situ hybridization.

Mrna sequence code#

We have studied in mammalian cells the nuclear export of mRNAs that code for secretory proteins, which are targeted to the endoplasmic reticulum membrane by hydrophobic signal sequences. In eukaryotic cells, most mRNAs are exported from the nucleus by the transcription export (TREX) complex, which is loaded onto mRNAs after their splicing and capping.