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Journal of Virology, May 2005, p. 6392-6399, Vol. 79, No. 10
0022-538X/05/$08.00+0 doi:10.1128/JVI.79.10.6392-6399.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Stephen A. Morris,1,
Wayne Chung,2
Paul D. Bieniasz,2 and
Myra O. McClure1*
Jefferiss Research Trust Laboratories, Wright-Fleming Institute, Faculty of Medicine, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, United Kingdom,1 Aaron Diamond AIDS Research Center and The Rockefeller University, New York, New York2
Received 24 August 2004/ Accepted 8 December 2004
Sequence motifs (L domains) have been described in viral structural proteins. Mutations in these lead to a defect at a late stage in virus assembly and budding. For several viruses, recruitment of an endosomal sorting complexes required for transport 1 subunit (Tsg101), a component of the class E vacuolar protein sorting (EVPS) machinery, is a prerequisite for virion budding. To effect this, Tsg101 interacts with the PT/SAP L domain. We have identified candidate L-domain motifs, PSAP, PPPI, and YEIL, in the prototypic foamy virus (PFV) Gag protein, based on their homology to known viral L domains. Mutation of the PSAP and PPPI motifs individually reduced PFV egress, and their combined mutation had an additive effect. When PSAP was mutated, residual infectious PFV release was unaffected by dominant negative Vps4 (an ATPase involved in the final stages of budding), and sensitivity to dominant negative Tsg101 was dramatically reduced, suggesting that the PSAP motif functions as a conventional class E VPS-dependent L domain. Consistent with this notion, yeast two-hybrid analysis showed a PSAP motif-dependent interaction between PFV Gag and Tsg101. Surprisingly, PFV release which is dependent on the PPPI motif was Vps4-independent and was partially inhibited by dominant negative Tsg101, suggesting that PPPI functions by an unconventional mechanism to facilitate PFV egress. Mutation of the YEIL sequence completely abolished particle formation and also reduced the rate of Gag processing by the viral protease, suggesting that the integrity of YEIL is required at an assembly step prior to budding and YEIL is not acting as an L domain.
G.S.P and S.A.M contributed equally to this work.
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