Fig. 2. Karyopherin-mediated nuclear RNA export pathways. This schematic provides an overview of the key factors involved in mediating the nuclear export of different classes of non-coding RNA, as well as the minor class of mRNAs that use the Crm1 nuclear export factor. Hypothetical factors that remain to be identified are indicated by `X'. In addition to late HIV mRNAs, a small number of cellular mRNAs may also be exported from the nucleus in a Crm1-dependent manner. Candidate cellular Rev-like adapter proteins include APRIL, pp32 and NXF3. The nuclear export pathway used by VA RNAs is also used by other small, non-coding RNAs including Y RNAs and, possibly, pre-miRNAs.