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Evidence for involvement of a nuclear envelope-associated RNA helicase activity in nucleocytoplasmic RNA transport
H C Schröder1, D Ugarkovic, P Langen
1Institut für Physiologische Chemie, Universität, Mainz, Federal Republic of Germany.
Abstract:
It seems well established that translocation of at least some mRNAs through the nuclear pore is (1) an energy-dependent process, and (2) dependent on the presence of the poly(A) segment attached to most mRNA species. We describe that RNA helicase (RNA duplex unwindase) activity is present in a nuclear envelope (NE) preparation, which also appears to be involved in nucleocytoplasmic RNA transport. This activity unwinds RNA: RNA hybrids. The helicase has a pH optimum of 7.5 and a temperature optimum of 30 degrees C. Applying the sealed NE vesicle system, it was shown that duplex RNA species are readily released from the vesicles in an unidirectional manner, in contrast to single-stranded RNA, which is much slower transported into the extravesicular space. Attachment of a poly(A) segment to the RNA duplex additionally increases the efflux rate of this RNA. Efflux of duplex RNA but not efflux of single-stranded RNA was strongly inhibited by formycin B 5'-triphosphate. Our results suggest that, besides poly(A), duplex structures, if present in a given RNA, modulate and control the export of RNA.
Insights
Nuclear pore translocation of mRNA involves energy and poly(A) tails. A nuclear envelope RNA helicase unwinds RNA duplexes, facilitating export, especially when polyadenylated.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Nuclear pore complex (NPC) mediated nucleocytoplasmic transport is essential for gene expression.
- mRNA export from the nucleus to the cytoplasm is a complex, regulated process.
- The role of RNA structure in nucleocytoplasmic transport is not fully understood.
Purpose of the Study:
- To investigate the role of RNA helicase activity in the nuclear envelope (NE).
- To determine the influence of RNA duplex structures and poly(A) segments on RNA export.
- To identify factors modulating RNA translocation through the nuclear pore.
Main Methods:
- Preparation of nuclear envelope (NE) vesicles.
- Assay of RNA helicase (RNA duplex unwindase) activity.
- Measurement of RNA efflux from NE vesicles.
- Inhibition studies using formycin B 5'-triphosphate.
Main Results:
- RNA helicase activity was detected in the NE, capable of unwinding RNA:RNA hybrids.
- Duplex RNA, particularly when polyadenylated, showed increased unidirectional efflux from NE vesicles.
- Formycin B 5'-triphosphate specifically inhibited duplex RNA efflux, but not single-stranded RNA efflux.
Conclusions:
- Nuclear envelope RNA helicase activity plays a role in nucleocytoplasmic RNA transport.
- RNA duplex structures, in addition to poly(A) tails, significantly influence and control RNA export.
- These findings provide new insights into the mechanisms regulating mRNA translocation through the nuclear pore.