Fig. 11.31  Model for passage of mRNPs through the nuclear pore complex.  After the coiled mRNP moves through the terminal ring, it uncoils as it passes through the central plug of the NPC, with the 5' end leading the way and becoming associated with ribosomes in the cytoplasm.

Fig. 11.33  Proposed mechanism for the transport of "cargo" proteins from the nucleus to the cytosol.  Exportin 1 binds to the NES of the cargo protein to be transported and to Ran-GTP. Hydrolysis of GTP in cytoplasm releases protein and Exportin 1 and Ran-GDP return to nucleus where Ran is regenerated to Ran-GTP.

Fig. 11.34  Proposed mechanism for mRNA export from the nucleus.  (a) The 5' end of the fully processed mRNA-hnRNP protein comples associated with cap-binding comples (CBC) which passes through the nuclear pore complex (NPC).  (b) Only proteins containing nuclear export signals (NES) transport mRNA from nucleus. (c) Hydrolysis of GTP dissociates hnRNPs from mRNA and allows re-entry of hnRNPs back into the nucleus.

Fig. 11.37  Proposed mechanism for the transport of "cargo" proteins containg a nuclear-localization signal (NLS) from the cytoplasm to the nucleus.

Fig. 11.38  Regulation of mRNA transport from the nucleus to the cytoplasm by the HIV Rev protein.  The HIV transcripts can be spliced into several alternative forms.  The Rev protein selectively improves transport of un-spliced and singly-spliced mRNA from the nucleus by binding at the Rev response element (RRE) in the HIV mRNA.