s (Table 2) and present as two copies in several group-Ⅱ NPVs, deletion of this ORF does not notably affect the virulence of the virus (248).
Ac137: p10, fibrillin or fibrous body protein
The p10 gene is a non-essential, hyper-expressed very late gene, encoding a 10.3 kDa protein (94 aa). P10 forms two cytoskeletal-like structures: microtubule-associated filaments through interaction with α-tubulin and perinuclear, tubular aggregates (25, 218). The formation of these structures requires the N-terminal heptad repeat/coiled-coil domain of P10 (52). Other domains include a pro-line rich region and a positively-charged C-terminus. The nuclear filaments may play a role in occlusion body maturation via interaction with the polyhedral envelope. P10 also triggers the release of individual polyhedra from the cell nucleus (265). The p10 promoter is-besides the polyhedrin promoter-exploited in baculovirus expression vectors.
Ac138: p74, occlusion-derived virus envelope protein
The AcMNPV P74 (73.9 kDa, 645 aa) was the first ODV-envelope protein found to be essential for primary infection in larval midguts (67) and is therefore also addressed as PIF-0 (review in (249)). The p74 gene belongs together with pif-1, pif-2 and pif-3 to the baculovirus core genes. In order to be active, P74 needs to be cleaved by trypsins in the insect gut (250). P74 is exposed at its N-terminus at the ODV surface and binds to midgut epithelium (89) through a receptor not yet characterized for AcMNPV. A double C-terminal membrane anchor allows insertion into membranes, as shown by rescue of P74 negative ODVs with recombinant P74 protein (293).
Ac139: me53, DNA synthesis regulator
The me53 ORF is an immediate-early gene abundantly transcribed as early as 1 h p.i. It encodes a protein of 53 kDa (52.6 kDa, 449 aa) with a C-terminal zinc finger motif (CX2CX13CX2C) suggesting a sequence-specific DNA binding capacity and the N-terminus contains a proline-rich region (131). Deletion of this essential gene prevents DNA replication (285).
Ac140; ac140, unknown 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, transc