gag
Domain
Gag polyprotein
Late-budding domains (L domains) are short sequence motifs essential for viral particle budding. They recruit proteins of the host ESCRT machinery (Endosomal Sorting Complex Required for Transport) or ESCRT-associated proteins. RNA-binding phosphoprotein p12 contains one L domain: a PPXY motif which interacts with the WW domain 3 of NEDD4 E3 ubiquitin ligase. PPXY motif is essential for virus egress. Matrix protein p15 contains one L domain: a PTAP/PSAP motif, which interacts with the UEV domain of TSG101. The junction between the matrix protein p15 and RNA-binding phosphoprotein p12 also contains one L domain: a LYPX(n)L motif which interacts with PDCD6IP. Both PSAP and LYPX(n)L domains might play little to no role in budding and possibly drive residual virus release.
Function
Gag polyprotein
Plays a role in budding and is processed by the viral protease during virion maturation outside the cell. During budding, it recruits, in a PPXY-dependent or independent manner, Nedd4-like ubiquitin ligases that conjugate ubiquitin molecules to Gag, or to Gag binding host factors. Interaction with HECT ubiquitin ligases probably links the viral protein to the host ESCRT pathway and facilitates release.
Matrix protein p15
Targets Gag and gag-pol polyproteins to the plasma membrane via a multipartite membrane binding signal, that includes its myristoylated N-terminus. Also mediates nuclear localization of the pre-integration complex.
RNA-binding phosphoprotein p12
Constituent of the pre-integration complex (PIC) which tethers the latter to mitotic chromosomes.
Capsid protein p30
Forms the spherical core of the virion that encapsulates the genomic RNA-nucleocapsid complex.
Nucleocapsid protein p10-Gag
Involved in the packaging and encapsidation of two copies of the genome. Binds with high affinity to conserved UCUG elements within the packaging signal, located near the 5'-end of the genome. This binding is dependent on genome dimerization.
Post-translational modifications
Gag polyprotein
Ubiquitinated by ITCH. Gag can recruit the ubiquitin ligase Itch in an L domain-independent manner to facilitate virus release via a mechanism that involves Gag ubiquitination.
Gag polyprotein
Specific enzymatic cleavages by the viral protease yield mature proteins. The protease is released by autocatalytic cleavage. The polyprotein is cleaved during and after budding, this process is termed maturation.
Capsid protein p30
Sumoylated; required for virus replication.
RNA-binding phosphoprotein p12 is phosphorylated on serine residues.
Cellular localization
- Gag polyprotein
- Virion
- Host cell membrane
- Lipid-anchor
- Host late endosome membrane
- Lipid-anchor
- Host endosome
- Host multivesicular body
- These locations are probably linked to virus assembly sites.
- Matrix protein p15
- Virion
- Capsid protein p30
- Virion
- Nucleocapsid protein p10-Gag
- Virion
- RNA-binding phosphoprotein p12
- Host cytoplasm
- Localizes to the host cytoplasm early in infection and binds to the mitotic chromosomes later on.
Alternative names
Gag polyprotein, Pr65gag, Core polyprotein, gag