ction of the insect host to allow efficient spread of OBs (96). V-CATH is also activated by chaotropic agents like SDS and its activity is inhibited by the protease inhibitor E64 (103). As, the chiA genes, the v-cath genes are also present in many Alphabaculoviruses and some Betabaculoviruses, but not all these viruses have both chiA and v-cath genes (Table 2 and Table 3).
Ac128: gp64, major budded virus envelope glycoprotein
In AcMNPV-infected Sf9 cells, the gene gp64 is transcribed both early and late in infection (116). GP64 (58.6 kDa predicted size, 512 aa) is absolutely essential for cell to cell spread of BVs. GP64 occurs as a covalently bonded trimer and is present on the surface of infected cells and is acquired by virions during budding through the plasma membrane, the final step in the release of BVs (212). GP64 is involved in host-receptor binding and is sufficient alone to mediate low-pH-triggered membrane fusion during intra-cellular trafficking (177). A domain in the N-terminal part (aa 21-159) is thought to be involved in host-receptor binding (292) and fusion and oligomerization domains have also been identified (192). The GP64 transmembrane region plays a crucial role in membrane fusion and is also required for GP64 trafficking and the budding process (154). The crystal structure of the GP64 post-fusion form revealed structural homology with the vesicular stomatitis virus G and herpes simplex virus type 1 gB proteins (121).
Ac129: p24, viral capsid protein
The gene ac129 is transcribed in the late phase of virus infection, initiated from a canonical late pro-moter sequence (GTAAG) situated immediately up-stream of the coding sequence (75). P24 (22.1 predicted molecular mass, 198 aa) is a capsid-associated protein, which is not N-glycosylated, but its precise function is unknown. Transposon-based interruption of the p24 gene did not affect viral propagation in cell culture (75, 242, 280). In SpltNPV, the homologous protein is associated with ODVs as a complex of 83 kDa (155). For Lymantria dispar (Ld)MNPV some natural variants lack p24 sequences (251).
Ac130: gp16, unknown function
Ac130 has the potential to encode a protein of 12.1 kDa (106 aa). In OpMNPV, the homologous protein GP16 was detected at 24 h p.i. and its levels increased through 120 h p.i. OpMNPV GP16 is N-glycosylated and not associated with purified BVs and ODVs. It localizes to cytoplasmic lamellar-like structures close to the nuclear membrane and to envelopes of viruses on their way from the nucleus to the cell surface (81). In AcMNPV, transcription of the gene ac130 could not be detected by microarray analysis (287).
Ac131: pp34, major polyhedral calyx protein
The phosphoprotein PP34 (38 kDa, predicted 29.1 kDa, 252 aa) is detected from 15 h p.i. and continues to be phosphorylated until 60-70 h p.i. inside infected insect cells. It is involved in the morphogenesis of the polyhedral envelope of baculoviruses and is part of the carbohydrate envelope of occlusion bodies called the calyx (278, 294). Electron-dense "spacers" present in wild-type AcMNPV-infected cells, are absent in pp34-null mutants (294).
Ac132: ac132, unknown function
The ac132 gene with a predicted product of 25.1 kDa (219 aa) is transcribed (287) and homologs are present in genomes of several other members of the genus Alphabaculovirus (Table 2), but no function has been associated with it.
Ac133: an, alkaline nuclease
All sequenced baculovirus genomes encode a homolog of alkaline nuclease (AN) (Table 2 and Table 3). The predicted molecular mass of the AcMNPV AN is 48.3 kDa (419 aa). AN protein is present in two forms, one full length (53 kDa) and a shorter form (43 kDa). Both forms are found at low levels from 12 h p.i., with maximal abundance at 24 h p.i. (150). AN associates with LEF-3, the baculovirus ssDNA-binding protein (185). AN has 5' to 3'exonuclease and 5' to 3' endonuclease activity. Both these enzyme functions are involved in DNA recombination and replication (185, 186). The first attempt to produce an AcMNPV an-null virus was not successful, suggesting that