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doi: 10.1242/10.1242/jcs.00268

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Nuclear RNA export

Howard Hughes Medical Institute and Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710, USA

View larger version (29K): [in a new window]   Fig. 1. The Ran-GTP gradient governs the directionality of nucleocytoplasmic transport mediated by members of the karyopherin family of nuclear transport factors. The key role played by the GTP-bound form of Ran in mediating cargo binding and release by karyopherins functioning in nuclear import (importins) or nuclear export (exportins) is illustrated. See text for more detailed discussion. Imp, importin; Exp, exportin.

View larger version (26K): [in a new window]   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.

View larger version (18K): [in a new window]   Fig. 3. Key factors involved in bulk mRNA export in metazoan cells. Recruitment of UAP56 to mRNA molecules, either by splicing or possibly via one of the other indicated mechanisms, likely represents the key initial step in inducing nuclear mRNA export. UAP56 may then recruit Aly, which in turn binds the Tap-Nxt nuclear RNA export factor. The MPMV CTE RNA binds the Tap-Nxt heterodimer directly, thus obviating the need for upstream factors. UAP56, Tap and Nxt are all essential for bulk mRNA nuclear export, but Aly is not, thus implying that a second, unknown factor may also mediate recruitment of the Tap-Nxt heterodimer by mRNA-bound UAP56 molecules.