[Nuclear export of viral RNAs in metazoan]

The nuclear export of mRNAs is a complex process, involving the participaton of numerous proteins, the recruitement of which starts during the early steps of mRNAs biosynthesis and maturation. This strategy allows the cell to export only mature and non-defective transcripts to the cytoplasm where they are directed to the translational machinery. The vast majority of mRNAs is exported by the dimeric transport receptor TAP-p15, which is mainly recruited by the large multiprotein complex TREX-1. Other mRNAs that do not display all typical features of a mature transcript use variants of the TAP-p15 export pathway or recruit the alternative export receptor CRM1. Most DNA viruses, retroviruses, and influenza viruses, the mRNAs of which are synthesized in the nucleus, also use TAP-p15 and/or CRM1 to export their mRNAs. The highjacking of the cellular export machinery by viral mRNAs usually involves the presence of constitutive structural elements that directly load cellular export factors and/or viral adaptor proteins. Associated with the host export machinery, viral mRNAs escape host surveillance, are efficiently exported in the cytoplasm in order to be translated, and thus make possible the progress toward the later events of the virus life cycles.