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The constitutive transport element (CTE) of Mason-Pfizer monkey virus (MPMV) accesses a cellular mRNA export pathway
A E Pasquinelli1, R K Ernst, E Lund
1Department of Biomolecular Chemistry, 1300 University Avenue, University of Wisconsin, Madison, WI 53706, USA.
Abstract:
The constitutive transport elements (CTEs) of type D retroviruses are cis-acting elements that promote nuclear export of incompletely spliced mRNAs. Unlike the Rev response element (RRE) of human immunodeficiency virus type 1 (HIV-1), CTEs depend entirely on factors encoded by the host cell genome. We show that an RNA comprised almost entirely of the CTE of Mason-Pfizer monkey virus (CTE RNA) is exported efficiently from Xenopus oocyte nuclei. The CTE RNA and an RNA containing the RRE of HIV-1 (plus Rev) have little effect on export of one another, demonstrating differences in host cell requirements of these two viral mRNA export pathways. Surprisingly, even very low amounts of CTE RNA block export of normal mRNAs, apparently through the sequestration of cellular mRNA export factors. Export of a CTE-containing lariat occurs when wild-type CTE, but not a mutant form, is inserted into the pre-mRNA. The CTE has two symmetric structures, either of which supports export and the titration of mRNA export factors, but both of which are required for maximal inhibition of mRNA export. Two host proteins bind specifically to the CTE but not to non-functional variants, making these proteins candidates for the sequestered mRNA export factors.
Insights
Constitutive transport elements (CTEs) from retroviruses efficiently export mRNA using host factors. CTEs can also sequester cellular export factors, inhibiting normal mRNA export.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Constitutive transport elements (CTEs) are cis-acting elements crucial for nuclear mRNA export in certain retroviruses.
- Unlike HIV-1's Rev response element (RRE), CTEs rely solely on host cell machinery for function.
Purpose of the Study:
- To investigate the mechanism of CTE-mediated mRNA nuclear export.
- To compare CTE and RRE export pathways and identify host factors involved.
Main Methods:
- Utilizing Xenopus oocytes as an experimental system.
- Employing RNA export assays with CTE and RRE constructs.
- Analyzing the effect of CTE RNA on normal mRNA export.
- Identifying host proteins that bind to CTEs.
Main Results:
- CTE RNA is efficiently exported from Xenopus oocyte nuclei.
- CTE and RRE pathways exhibit distinct host cell requirements.
- CTE RNA can inhibit the export of normal cellular mRNAs by sequestering export factors.
- A CTE-containing lariat is exported when a functional CTE is present.
- Two host proteins specifically bind to functional CTEs, suggesting their role in export.
Conclusions:
- CTEs utilize host cell factors for mRNA export.
- CTEs can interfere with cellular mRNA export by sequestering essential factors.
- The identified host proteins are potential candidates for mediating CTE-dependent export.