A nuclear export signal within the structural Gag protein is required for prototype foamy virus replication.
BACKGROUND
The Gag polyproteins play distinct roles during the replication cycle of retroviruses, hijacking many cellular machineries to fulfill them. In the case of the prototype foamy virus (PFV), Gag structural proteins undergo transient nuclear trafficking after their synthesis, returning back to the cytoplasm for capsid assembly and virus egress. The functional role of this nuclear stage as well as the molecular mechanism(s) responsible for Gag nuclear export are not understood.


RESULTS
We have identified a leptomycin B (LMB)-sensitive nuclear export sequence (NES) within the N-terminus of PFV Gag that is absolutely required for the completion of late stages of virus replication. Point mutations of conserved residues within this motif lead to nuclear redistribution of Gag, preventing subsequent virus egress. We have shown that a NES-defective PFV Gag acts as a dominant negative mutant by sequestrating its wild-type counterpart in the nucleus. Trans-complementation experiments with the heterologous NES of HIV-1 Rev allow the cytoplasmic redistribution of FV Gag, but fail to restore infectivity.


CONCLUSIONS
PFV Gag-Gag interactions are finely tuned in the cytoplasm to regulate their functions, capsid assembly, and virus release. In the nucleus, we have shown Gag-Gag interactions which could be involved in the nuclear export of Gag and viral RNA. We propose that nuclear export of unspliced and partially spliced PFV RNAs relies on two complementary mechanisms, which take place successively during the replication cycle.
CNRS UMR7212, Inserm U944, Université Paris Diderot, Institut Universitaire d'Hématologie, Paris, France.
Noémie
N
Renault
Joelle
J
Tobaly-Tapiero
Joris
J
Paris
Marie-Lou
ML
Giron
Audrey
A
Coiffic
Philippe
P
Roingeard
Ali
A
Saïb
D002467:Cell Nucleus / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D015683:Gene Products, gag / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D015497:HIV-1 / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D016297:Mutagenesis, Site-Directed; D049790:Nuclear Export Signals; D017354:Point Mutation; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D053150:Simian foamy virus / Q000502:physiology*; D014779:Virus Replication; D054321:rev Gene Products, Human Immunodeficiency Virus / Q000737:chemistry / Q000378:metabolism
D005231:Fatty Acids, Unsaturated; D015683:Gene Products, gag; D049790:Nuclear Export Signals; D011993:Recombinant Fusion Proteins; D054321:rev Gene Products, Human Immunodeficiency Virus; C514860:rev protein, Human Immunodeficiency Virus-1; C038753:leptomycin B
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