Nucleic Acids Research Advance Access originally published online on October 3, 2008
Nucleic Acids Research 2008 36(19):6284-6294; doi:10.1093/nar/gkn608
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Nucleic Acids Research, 2008, Vol. 36, No. 19 6284-6294
© 2008 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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Identification of the Rem-responsive element of mouse mammary tumor virus
1Department of Pathobiology, Institute of Virology, University of Veterinary Medicine Vienna, 2Christian-Doppler Laboratory for Gene Therapeutic Vector Development and 3Austrianova Biotechnology GmbH, Vienna, A-1210, Austria
*To whom correspondence should be addressed. Tel: +43 1250772333; Fax: +43 1250772690; Email: stanislav.indik{at}vu-wien.ac.at
Received June 16, 2008. Revised September 8, 2008. Accepted September 8, 2008.
Mouse mammary tumor virus (MMTV) has previously been shown to encode a functional homolog of the human immunodeficiency virus-1 (HIV-1) nuclear export protein Rev, termed Rem. Here, we show that deletion of the rem gene from a MMTV molecular clone interfered with the nucleo-cytoplasmic transport of genomic length viral mRNA and resulted in a loss of viral capsid (Gag) protein production. Interestingly, nuclear export of single-spliced env mRNA was only moderately affected, suggesting that this transcript is, at least to some extent, transported via a distinct, Rem-independent export mechanism. To identify and characterize a cis-acting RNA element required for Rem responsiveness (RmRE), extensive computational and functional analyses were performed. By these means a region of 490 nt corresponding to positions nt 8517–nt 9006 in the MMTV reference strain was identified as RmRE. Deletion of this fragment, which spans the env-U3 junction region, abolished Gag expression. Furthermore, insertion of this sequence into a heterologous HIV-1-based reporter construct restored, in the presence of Rem, HIV-1 Gag expression to levels determined for the Rev/RRE export system. These results clearly demonstrate that the identified region, whose geometry resembles that of other retroviral-responsive elements, is capable to functionally substitute, in the presence of Rem, for Rev/RRE and thus provide unequivocal evidence that MMTV is a complex retrovirus.