ribed from the same promoter motifs as odv-e18 (ac143) and its product, ODV/EC27, is localized to the ODV envelope and capsid structures (19). The protein has a cyclin-like domain, suggesting a role in cell cycle de-regulation (13). Antibodies against ODV-EC27 recognized a 27 kDa protein (33.5 kDa predicted, 292 aa) in infected cells and proteins of 27 and 35 kDa in purified ODVs. The ODV-E35 protein appears to be the result of a translational shift during ribosomal reading of the bicistronic odv-e18/odv-27 mRNA (19). ODV-E27 interacts with ODV/BV-C42 and P78/83 (18). AcMNPV odv-e27 deletion mutants show a diminished production of infectious BVs. DNA replication is similar as for the wild-type virus but the mutant has a defect in nucleocapsid assembly (270). Odv-ec27 is a baculovirus core gene.
Ac145: ac145, unknown function
The gene ac145 is expressed at the late to very late phase of infection and encodes a small protein (8.9 kDa, 77 aa), present in both BVs and ODVs. Ac145 belongs to a family of proteins, which contain a C6 or peritrophin-A-like domain (CX7-18CX5CX6-11CX12CX5-11C, where X represents any amino acid residue other than cysteine) (143). The function of Ac145 is not clear although it plays a role in oral infection. Deletion of ac145 does not affect BV propagation, but leads to decreased in vivo infectivity compared to wild-type AcMNPV in a host dependent way (143). Homologs of the gene are conserved in all baculoviruses, except Deltabaculoviruses (Table 2 and Table 3).
Ac146: ac146, unknown function
The ac146 gene codes for a protein of 22.9 kDa (201 aa) and is found in the genomes of Alpha-and Betabaculoviruses. No information about the function of ac146 is available.
Ac147: ie-1, immediate early transactivator IE-1
During the early phase of infection, mRNAs of 1.9-kb and spliced 2.1-kb transcripts are present which encode IE-1 and IE-0, respectively (35). The ie-0 transcript is the only known spliced baculovirus mRNA. IE-1 contains 582 aa (66.9 kDa) arranged into different domains, including an acidic activation domain at the N-terminus, a DNA binding domain, and an oligomerization domain at the C-terminus (47, 136). Compared to IE-1, IE-0 has 52 extra N-terminal amino acids. IE-1 is a potent transcriptional transactivator and essential for virus replication (133). A virus lacking either ie-1 or ie-0 could be propagated in cell culture, but a double knock-out is not viable. The ie0-ie1 gene complex is essential for viral infection and is needed to obtain wild type levels of replication, late gene expression and BV and ODV production (243, 197). De novo synthesis of IE-1 leads to virus-induced apoptosis (252). IE-1 also transactivates the expression of the p35 gene, and in that way counteracts its own pro-apoptotic activity (243). Homologs are found in all Alphabaculoviruses (Table 2).
Ac148: odv-e56, occlusion-derived virus envelope protein
Transcription of the gene odv-e56 starts from a late ATAAG promoter and transcripts are detected from 16 to 72 h p.i. (17). ODV-E56 protein (predicted 40.9 kDa, 476 aa) is present in viral-induced intranuclear microvesicles, and consequently is incorporated into ODV envelopes (17). Mutation in the 3x-end of odv- e56 alters its location to the nucleocapsids instead of the ODV envelope, suggesting that an important localization sequence is present in the C-terminus of this protein (17).
Ac149: ac149, unknown function
The ac149 ORF encodes a putative protein of 12.4 kDa (107 aa) with unknown function. Homologs are present in a few related Alphabaculoviruses (Table 2).
Ac150: ac150, unknown function
The gene ac150 encodes an 11.2 kDa (99 aa) protein and is expressed in the late to very late phase of infection. The protein Ac150, is a member of a family containing peritrophin-A-like domains (see also ac145) -common among mucins, peritrophins and chitinases -and the protein contains an integrin-binding motif (143). Deletion of ac150 has no effect on infectivity of the virus for T. ni or H. virescens larvae, but the mutant is less efficient in establishing a primary infectio