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Other Viral Proteins
ОглавлениеVirus particles may also contain additional viral proteins that are not enzymes but nonetheless are important for an efficient infectious cycle. Among the best characterized are the protein primers for viral genome replication that are covalently linked to the genomes of picornaviruses such as poliovirus and adenoviruses. Others include several tegument proteins of herpesviruses, such as the VP16 protein, which activates transcription of viral immediate-early genes to initiate the viral program of gene expression. The cores of vaccinia virus also contain proteins that are essential for transcription of viral genes, as they allow recognition of viral early promoters. Other herpesvirus tegument proteins induce the degradation of cellular mRNA or block cellular mechanisms by which viral proteins are presented to the host’s immune system. Retroviruses with complex genomes, such as human immunodeficiency virus type 1, contain additional proteins required for efficient viral reproduction in certain cell types. These proteins are discussed in Volume II, Chapter 12.
Table 4.3 Some virion enzymes
| Virus | Protein | Function(s) |
|---|---|---|
| Adenovirus | ||
| Human adenovirus type 2 | L3 23k | Protease; production of infectious particles |
| Herpesvirus | ||
| Herpes simplex virus type 1 | VP24 | Protease; capsid maturation for genome encapsidation |
| UL13 | Protein kinase | |
| Vhs | RNase | |
| Orthomyxovirus | ||
| Influenza A virus | P proteins | RNA-dependent RNA polymerase; synthesis of viral mRNA and vRNA; cap-dependent endonuclease |
| Poxvirus | ||
| Vaccinia virusa | DNA-dependent RNA polymerase (8 subunits) | Synthesis of viral mRNA |
| Poly(A) polymerase (2 subunits) | Synthesis of poly(A) on viral mRNA | |
| Capping enzyme (2 subunits) | Addition of 5' caps to viral pre-mRNA | |
| DNA topoisomer ase | Sequence-specific nicking of viral DNA | |
| Proteases 1 and 2 | Virus particle morphogenesis | |
| Reovirus | ||
| Reovirus type 1 | λ2 | Guanylyltransferase |
| λ3 | Double-stranded RNA-dependent RNA polymerase | |
| Retrovirus | ||
| Human immunodeficiency virus | Pol | Reverse transcriptase; proviral DNA synthesis |
| type 1 | ||
| IN | Integrase; integration of proviral DNA into the cellular genome | |
| PR | Protease; production of infectious particles | |
| Rhabdovirus | ||
| Vesicular stomatitis virus | L | RNA-dependent RNA polymerase; synthesis of viral mRNA and vRNA |
aVaccinia virions contain some 20 enzymes, only a few of which are listed.
