9, major viral capsid protein VP39
The VP39 (39.0 kDa, 357 aa) is the most abundant structural protein of the nucleocapsid (260) with monomers arranged in stacked rings around the nucleoprotein core as reviewed in (249). VP39 is involved in the rearrangement and polymerization of host actin (28, 29). Recent results have shown that VP39 interacts with the 38K protein in infected insect cells (281). The vp39 gene is transcribed at late time points in infection from a promoter sequence containing three A/GTAAG consensus motifs (maximal transcription 12-24 h p.i.) as a bicistronic mRNA together with cg30 (259, 260). Vp39 is a core gene.
Ac90: lef-4, late expression factor 4
The lef-4 gene encodes the 55 kDa late expression factor 4 (predicted molecular mass 53.9 kDa, 464 aa) (54). LEF-4 is a subunit of the AcMNPV RNA polymerase (88) (see ac40) and is essential for late gene expression (132). LEF-4 has guanylyltransferase (84), RNA 5'-triphosphatase and ATPase activities (119), and appears to be a complete mRNA capping enzyme. The lef-4 gene is present in all baculoviruses (Table 2 and Table 3).
Ac91: ac91, unknown function
Ac91 potentially encodes a 24.1 kDa (224 aa) protein expressed in the late phase of infection and the gene is transcribed (287). The protein has an N-terminus rich in hydrophobic amino acids, including a stretch of 7 isoleucine residues, and a large central domain consisting of mainly proline, threonine and serine residues. The C-terminal domain, which is preceded by a methionine, is also present in some other baculovi-ruses, suggesting that the protein encoding region may be smaller than the entire ORF (not published).
Ac92: ac92/p33, unknown function, P33
Ac92 is a baculovirus core gene encoding a 33 kDa (predicted 30.9 kDa, 259 aa) protein (P33). Inactivation of this gene is lethal for the virus, indicating that ac93 is an essential baculovirus gene (230). P33 forms a complex with the mammalian tumor suppressor protein P53, when AcMNPV is used as a p53 gene expression vector, P33 also enhances P53-mediated apoptosis in insect cells (230). Flag-tagged P33 displays a diffuse cytoplasmic localization and punctuate nuclear staining in the absence of P53. In the presence of P53, P33 has an entirely nuclear localization. An insect p53 homolog has been identified (208) and many DNA viruses encode a P53 binding protein. Mass spectrometry indicated that P33 may be present in ODV particles (20).
Ac93: ac93, unknown function
The ac93 ORF is transcribed (287) and encodes a 18.4 kDa (161 aa) protein of unknown function, also named P18 in other baculoviruses. The conserved region is addressed as a DUF628 domain in the CDD (176).
Ac94: odv-e25, occlusion-derived virus envelope protein
ODV-E25 (25.5 kDa, 228 aa) is an integral ODV envelope protein, that is N-terminally anchored in the envelope (249). ODV-E25 is also present in BVs, but is much less abundant there than in ODVs (239). The ODV-E25 protein is initially present at a low concentrations, but is present at a higher levels from 36 h p.i. onwards (239). The N-terminal amino acid sequence of the protein (24 amino acids) is highly hydrophobic and this hydrophobic domain is sufficient to direct ODV-E25 to virus-induced membrane micro-vesicles within the nucleus and the ODV viral envelope (104).
Ac95: helicase, DNA helicase
Ac95 is a baculovirus core gene and encodes a 143.2 kDa (1221 aa) polypeptide (P143) with a consensus NTP-binding site and six other motifs characteristic for helicase proteins. Ac95 is a delayed early gene, which is transactivated by IE-1 (ac147) and PE38 (ac153) with a stimulatory role of IE-2 (ac151) (163). A ts-mutant showed the essential role of P143 in viral DNA replication (165) and this was further confirmed by transient replication assays (133). The AcMNPV helicase shows specificity for AcMNPV replication and cannot be exchanged with the SeMNPV helicase in transient DNA replication assays (98).
Ac96: ac96, unknown function
Ac96 is a baculovirus core gene encoding a 19.8 kDa (173 aa) protein. The BmNPV homolog Bm79 encodes a larger, 28 kD