Joining the dots: production, processing and targeting of U snRNP to nuclear bodies.

The spliceosome is the RNP complex than catalyses the removal of introns from the Uridine-rich small nuclear ribonucleoproteins (U snRNPs) that make up the main components of this complex. The production of these RNPs is an intricate process, involving several key stages. These include: 1) the transcription of the U snRNAs; 2) their nuclear export; 3) the cytoplasmic assembly of the U snRNP; 4) their nuclear import; 5) their processing within Cajal bodies and the nucleolus; and 6) their storage in interchromatin granule clusters (IGCs). This review focuses on each of these stages, discussing the key complexes involved as well as the trafficking and targeting mechanisms involved.