Quality control of messenger ribonucleoprotein particles in the nucleus and at the pore.

The spatial separation of nuclear transcription and cytoplasmic translation in eukaryotic cells implies that mRNAs have to travel. On their journey, proteins involved in the various steps of transcript formation, processing and transport dynamically interact with mRNAs to form diverse messenger ribonucleoprotein complexes (mRNPs). Increasing evidence indicates that the protein complexes involved in distinct phases of manufacturing a bona fide mRNA in the nucleus are tightly coupled. Moreover, the recent demonstration that active genes migrate into preassembled, shared nuclear sub-compartments suggests that mRNAs are churned out in large 'transcription factories' with distinct but interconnected divisions. Nuclear factors have now been identified that specifically control the quality of mRNAs without affecting mRNP biogenesis or export.