(NAS Colloquium) Molecular Kinesis in Cellular Function and Plasticity (2002) / Chapter Skim
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Pages 16-21
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From page 16... ...
The completed RNP particle is released into the nucleoplasm and transported to the nuclear pore, where the RNP fibril is gradually unfolded and passes through the pore. On the cytoplasmic side, the exiting extended RNP fibril becomes engaged in protein synthesis and the ensuing polysome is anchored to the endoplasmic reticulum.
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From page 17... ...
(19~. The translocation process has been studied in detail, and several discrete steps have been elucidated: binding of the BR RNP particle to the nucleoplasmic fibers of the nuclear pore complex, docking of the particle in front of the central channel of the pore complex, unrolling of the ribbon and translocation of the RNP complex with its 5' end in the lead through the channel, exit of the unfolded RNP fibril into the cytoplasm, and formation of a polysome just outside the pore (8~.
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From page 18... ...
3. Assemblv and transport of the BR RNP particle and its relation to a number of BR RNA-associated proteins.
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From page 19... ...
It seems likely that the two proteins play important roles in the structural organization of the pre-mRNP particle, setting the stage for splicing rather than directly participating in the splicing process. The two proteins are not released at the same time in conjunction with the translocation of the BR particle through the nuclear pore: whereas hrp23 is shed just before or at the binding of the particle to the pore, hrp45 is released when the particle enters the central channel.
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From page 20... ...
Conclusions A specific transcription product, the BR RNP particle, has been studied during assembly on the gene and transport through the nucleoplasm to and through the nuclear pores. On the cytoplasmic side, the BR RNP particle appears as an extended RNP fibril that immediately engages in protein synthesis.
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From page 21... ...
(iii) The various proteins behave differently during RNA transport: some leave the transcript in the nucleoplasm or at the nuclear pore, others are shed subsequent to the translocation of the particle through the nuclear pore, whereas still others accompany the mRNA into polysomes.
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