Nuclear export of RNA.

A defining feature of eukaryotic cells is the presence of a nuclear envelope separating transcription and DNA replication in the nucleus from the site of protein synthesis in the cytoplasm. The regulation of gene expression relies in part on the controlled exchange of molecules between these two compartments. Factors implicated in transcription regulation and DNA replication have to be imported into the nucleus, whereas RNAs produced in the nucleus have to be exported, either to fulfill their function in protein synthesis or to mature into functional particles. This review summarizes studies performed over the last 15 years that led to the identification of cellular factors mediating nuclear export of the different classes of RNAs, including tRNAs, UsnRNAs, micro-RNAs, ribosomal RNAs and mRNAs. We also discuss recent evidence indicating that the nuclear transport step is intimately linked to RNA synthesis, processing and mRNP assembly, thus ensuring that only properly matured ribonucleoprotein (RNP) complexes reach the cytoplasm.