 an is an essential gene (150). Transfection with an AcMNPV an-null bacmid shows no BV production and a reduced number of normal-appearing nucleo-capsids. Instead, numerous aberrant capsid-like structures are formed, indicating a defect in nucleocapsid maturation or in a DNA-processing step, that is necessary for encapsidation (206, 207).
Ac134: 94k, unknown function
The 94k gene encodes a protein of 94.5 kDa (803 aa). The function of the 94K is still unknown, but homologs can be found in several other baculoviruses (Table 2 and 3). In the closely related BmNPV only 151 bps correspond to ac134 suggesting the gene might not be essential and was lost by a deletion (76). Random transposon insertions into the 94k gene have confirmed that it is not essential for virus replication (32). The 94k gene harbors the non-hr origin of replication, which is characterized by palindromes-and AT-rich regions. These motifs are essential for its ability to act as origin of DNA replication and are conserved in BmNPV (134).
Ac135: 35k/p35, apoptosis inhibitor
The gene p35 encodes the 34.8 kDa (299 aa) protein P35, which is a strong inhibitor of apoptosis The function of P35 and IAP proteins is extensively reviewed e.g. (36). Mutations in the p35 gene result in apoptosis of infected Sf21 cells and abort infection (37, 146), but have a wild type appearance in Tn368 cells (38). P35 blocks apoptosis by inhibiting the activity of Sf-caspase-1 and as such works at a different point in the caspase cascade as IAPs, which block apoptosis further upstream in the pathway (5, 140). Crystal structures of the interaction between P35 and Sf-caspase-1 have been determined (56). P35 gene expression is transactivated by IE-1 the protein, which is also responsible for inducing apoptosis (243).
Ac136: p26, unknown function
The gene p26 encodes a dimeric protein (monomeric 27.2 kDa, 240 aa) with unknown function, which is located primarily in the cytoplasm. Transcripts accumulate between 2-12 h p.i. (73, 248). Although conserved in most Alphabaculoviruses (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, unkn