Disease relevance of Virus Assembly

• Retrovirus assembly and maturation involve folding and transport of viral proteins to the virus assembly site followed by subsequent proteolytic cleavage of the Gag polyprotein within the nascent virion [1].
• Covalent linkage of myristic acid to the N-terminal glycine residue of Pr55gag, the precursor of the major structural proteins of human immunodeficiency virus 1 (HIV-1), facilitates an essential step in virus assembly and propagation [2].
• Phosphorylation of the polyomavirus major capsid protein VP1 plays a role in virus assembly and may function in virus-cell recognition [3].
• Cellular transcription factor Sp1 recruits simian virus 40 capsid proteins to the viral packaging signal, ses [4].
• To delineate the processes of virus assembly that mediate Vpx packaging, we used a recombinant vaccinia virus-T7 RNA polymerase system to facilitate Gag protein expression, particle assembly, and extracellular release [5].

High impact information on Virus Assembly

• During virus assembly, a subset of MA is phosphorylated on the C-terminal tyrosine by a virion-associated cellular protein kinase [6].
• High titer producer clones expressing ZAP-70 were generated in the Gibbon ape leukemia virus packaging line PG13 [7].
• Direct contact between hematopoietic cells and viral packaging cell lines or other sources of stroma has been shown to increase the efficiency of retroviral-mediated gene transfer into these target cells compared with infection with viral supernatant [8].
• In addition, we demonstrate that membrane association of wild-type VP40 also induces the conformational switch from monomeric to hexameric molecules that may form the building blocks for initiation of virus assembly and budding [9].
• The nucleocapsid-independent formation of apparently bona fide viral envelopes represents a novel mode of virus assembly [10].

Chemical compound and disease context of Virus Assembly

• A single deletion in the membrane-proximal region of the Sindbis virus glycoprotein E2 endodomain blocks virus assembly [11].
• The goal of these experiments was to determine the steps in virus assembly that are defective at the nonpermissive temperature in temperature-sensitive (ts) matrix (M) protein mutants of vesicular stomatitis virus [12].
• Histidine 39 in the dengue virus type 2 M protein has an important role in virus assembly [13].

Biological context of Virus Assembly

• Another mutant, MN1, which lacks amino acids 4 to 21 of M protein demonstrated that the abilities of M protein to inhibit chloramphenicol acetyltransferase gene expression and to localize to the nucleus were unaffected by deletion of this lysine-rich amino-terminal region but that the ability to function in virus assembly was ablated [14].
• In addition, the aspartic acid at position 111 in the HCV core protein sequence was found to be crucial for virus assembly, demonstrating the usefulness of this system for mapping amino acids critical to HCV morphogenesis [15].
• To investigate the role of HA palmitylation in virus assembly, we used reverse genetics technique to introduce substitutions and deletions that affected the three conserved cysteine residues into the H3 subtype HA [16].
• A mutation at matrix residue 62 reversed the effect of a position 34 change which blocks envelope glycoprotein incorporation into virions, and substitutions at residues 27 and 51 reversed the phenotype of a position 86 mutation which redirects virus assembly to the cytoplasm [17].
• These mutations do not impair virus assembly and release, RNA encapsidation, or envelope glycoprotein incorporation into virions but rather cause significant defects in an early step in the virus life cycle, as measured by single-cycle infectivity assays and the analysis of viral DNA synthesis early postinfection [18].

Anatomical context of Virus Assembly

• The results are consistent with the theory that myristate is required for the association of the gag protein with the plasma membrane and that this association is necessary for virus assembly [19].
• We hypothesize that this provides a control mechanism which ensures that the CP precursor is used for virus assembly in the cytoplasm and that only mature virus particles reach the nuclear pore [20].

Associations of Virus Assembly with chemical compounds

• Finally, we observed that a previously described matrix mutant, Myr1E, was insensitive to the effects of leptomycin B, apparently bypassing the nuclear compartment during virus assembly [21].
• As might be expected from this finding, viral protein synthesis accompanies virus assembly in actinomycin D-treated cells [22].
• Second, the resulting NH2-terminal 23-residue fragment is removed during virus assembly [23].
• The stage of virus assembly inhibited by colchicine and dibucaine was studied by experiments with [3H]-leucine or [35S]methionine [24].
• This demonstrates that virus assembly is possible in the absence of M; conversely, the cytoplasmic domain of F allows incorporation of M and enhances assembly [25].

Gene context of Virus Assembly

• Cellular functions that promote viral replication include the MAK3-encoded N-acetyltransferase whose modification of the gag N terminus is necessary for L-A virus assembly [26].
• These data indicate that VP24 possesses structural features commonly associated with viral matrix proteins and that VP24 may have a role in virus assembly and budding [27].
• The VP40 matrix protein of Ebola virus buds from cells in the form of virus-like particles (VLPs) and plays a central role in virus assembly and budding [28].
• Interestingly, expression of APOBEC3G in the presence of wild-type Vif not only affected viral packaging but also reduced its intracellular expression level [29].
• In contrast, Pr55gag expressed in the absence of Vpu was initially inserted into the plasma membrane, but subsequently endocytosed, and virus assembly was partially shifted to internal membranes [30].

Analytical, diagnostic and therapeutic context of Virus Assembly

• Immunofluorescence studies showed that p65 is localized to the sites of virus assembly [31].
• Thus, immunoprecipitation of cellular extracts showed that P60 was phosphorylated in both producer and nonproducer transformed cells, indicating that phosphorylation occurs independently of virus assembly [32].
• Transmission electron microscopy revealed regions of intranuclear recombinant virus assembly and the presence of numerous intracytoplasmic proteinaceous vesicular inclusions consistent with hyperproduction of hCB2 [33].

References