Identification of the Rem-responsive element of mouse mammary tumor virus

• Published in: Nucleic acids research 2008-11, Vol.36 (19), p.6284-6294
• Main Authors: Müllner, Matthias, Salmons, Brian, Günzburg, Walter H, Indik, Stanislav
• Format: Article
• Language: English
• Subjects: Active Transport, Cell Nucleus; Animals; Binding Sites; Cats; Cell Line; Cell Nucleus - metabolism; Computational Biology; gag Gene Products, Human Immunodeficiency Virus - genetics; gag Gene Products, Human Immunodeficiency Virus - metabolism; Genes, Reporter; HIV-1 - genetics; Human immunodeficiency virus 1; Mammary Tumor Virus, Mouse - genetics; Mouse mammary tumor virus; Regulatory Sequences, Ribonucleic Acid; RNA; RNA, Viral - chemistry; RNA, Viral - metabolism; RNA-Binding Proteins - metabolism; Sequence Deletion; Viral Proteins - metabolism
• ISSN: 0305-1048; 1362-4962
• DOI: 10.1093/nar/gkn608

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.