RNA export: insights from viral models.

The retroviruses export intron-containing RNA. The complex retroviruses encode a Rev protein that uses a leucine-rich NES to interact with CRM1 and the U snRNA-export pathway. Other viruses encode proteins with a Rev-like NES. The type-D retroviruses contain a CTE that binds the cellular protein TAP to export intron-containing RNA through the mRNA pathway. Intronless viral transcripts contain post-transcriptionally acting RNA elements that may compensate for the lack of an intron. The functions of elements in intronless RNA are not fully understood but may be in export and/or 3'-end processing.