The interplay of nuclear mRNP assembly, mRNA surveillance and export.

Fully processed mRNAs are exported to the cytoplasm where they direct protein synthesis. Export of mRNAs is mediated by a conserved heterodimeric transport receptor (known as NXF1-p15 in metazoa) that binds to mRNA cargoes either directly or indirectly by means of adaptor proteins. Upon binding, the receptor translocates the cargo across the central channel of the nuclear pore complex (NPC) by interacting directly with NPC proteins called nucleoporins. Our understanding of the molecular mechanisms by which the heterodimeric receptor is recruited to cellular mRNAs indicates that the adaptors, together with additional proteins, are loaded cotranscriptionally to nascent mRNAs to form large ribonucleoprotein complexes (mRNPs). This mRNP assembly process might be subject to quality control by a nuclear mRNP surveillance mechanism, so that aberrantly assembled mRNPs are degraded before the receptor delivers them to the cytoplasm.