own function
Ac141: exon0, unknown function
The gene exon0 is transcribed in the late phase of infection and encodes a 30.1 kDa (261 aa) protein with the following functional domains: The N-ter-minal halve of EXON-0 contains two acidic domains and a domain rich in charged amino acids, whereas the C-terminal part comprises a leucine zipper/coiled coil domain and a RING finger-like domain (46, 64). The protein EXON0 is not essential for virus replication or ODV production, but is required for the production of BVs, as it mediates the egress of nucleocapsids from the nucleus (46, 63). EXON0 interacts with the nucleocapsid protein BV/ODV-C42 and with FP25, enabling the escape of nucleocapsids from the nucleus to the cytoplasm (64). Recently, interaction of EXON0 with -tubulin was demonstrated (65). The ac141 ORF is located in the 4.5 kb part of the transcript that is removed by splicing to get the immediate early ie-0 mRNA (see ac147) (46). Some homologs are aberrantly referred to in literature as ie-0.
Ac142: 49k, 49 kDa protein
The ORF ac142 belongs to the core baculovirus genes and is a late gene, transcribed from 12 to 72 h p.i. The gene product, Ac142, is a 55.4 kDa (477-aa) protein with a putative transmembrane domain and is associated with the nucleopcapsids of BVs and ODVs (20, 178). ac142 is essential for infectious BV production and for effective envelopment of ODVs to allow the subsequent packaging into occlusion bodies (178).
Ac143: odv-e18, occlusion-derived virus envelope protein
The gene odv-e18 is transcribed from three late promoter motifs from 16 through 72 h p.i. ODV-E18 is a structural protein (6.6 kDa predicted, 62 aa) present in the ODV envelope and in virus-induced intranuclear membranes (19). Deletion of ac143 prohibits the production of infectious BVs, however, the level of DNA replication and occlusion body formation are not affected (179). Homologs are found in all baculovirus genomes (179).
Ac144: odv-ec27, occlusion-derived virus envelope/capsid protein
The odv-ec27 is a late gene, transcribed 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 a