te and very late gene promoters. HCF-1 is absolutely required for virus replication and late gene expression in TN-368 cells, and its absence is accompanied by a block in cellular and viral protein synthesis (170). In T. ni larvae a hcf-1 mutant, shows a reduced speed of kill. In Sf21 cells and in S. frugiperda larvae replication of hcf-1 mutants is not different from that of the wild type virus, hence the name host cell-specific factor (170).
Ac71: iap-2, apoptosis inhibitor
The gene iap-2 encodes a putative apoptosis inhibitor (28.6 kDa, 249 aa). It contains the conserved RING-finger like-motifs present in all iap genes, but not a BIR repeat region (79). Deletion of either iap-1 (ac27) or iap-2, or the simultaneous deletion of both genes did not have an effect on the replication of the virus in Sf21 cells (79). Whether it has a role in inhibiting apoptosis remains unclear. In other NPVs IAPs have been shown to inhibit apoptosis (36).
Ac72: unknown function
Ac73: ac73, unknown function
Homologs of the predicted gene ac73 (11.5 kDa, 99 aa protein) are present in genomes of several other members of the genus Alphabaculovirus (Table 2). Information about the (putative) function of ac73 in the viral life cycle is not available, but transcripts are made (287).
Ac74: ac74, unknown function
Ac75: ac75, unknown function
Homologs of ac75 can only be found in genomes of Alphabaculoviruses (Table 2). The predicted gene product has a molecular mass of 15.5 kDa (133 aa) and transcripts have been detected with micro-arrays (287). There is no publication about the role of ac75 in baculovirus biology.
Ac76; ac76, unknown function
Homologs of ac76 can be found in genomes of all Alphabaculoviruses (Table 2). The predicted gene is transcribed (287) and encodes a hypothetical protein of 9.4 kDa (84 aa). No data about the role of ac76 in the baculovirus replication cycle are available.
Ac77: vlf-1, very late expression factor 1
Ac77 or the vlf-1 gene is involved in the expression of the very late genes p10 and polh (183, 288). The gene is transcribed in the late phase of infection – from 15 to 24 h p.i. The VLF-1 protein (44.4 kDa, 379 aa) is localized in the nucleus of infected cells and in nucleocapsids of both BV and ODV (289). Deletion of the vlf-1 gene results in defective BV production, but this is not due to impaired DNA replication as the vlf-1 mutant is still able to replicate DNA, although at a lower level (268). When infected with a vlf-1 null mutant neither nucleocapsids nor occlusion bodies are produced (153). VLF-1 may be involved in viral DNA processing as the protein sequence of VLF-1 shows similarity to integrases and resolvases (153, 183). Integrases belong to a family of tyrosine recombinases, which can arrange DNA duplexes by site-specific recombination (60). DNA replication of most likely AcMNPV is based on concatemer formation (147) and if true, VLF-1 might be involved in processing the concatemers before the DNA is packaged into nucleocapsids (153). Ac77 is a baculovirus core gene.
Ac78: ac78, unknown function
The ac78 gene product is a hypothetical protein (12.5 kDa, 109 aa) with a conserved DUF912 domain (176), which occurs in homologous NPV proteins, but gives no indication for the function of ac78. The gene is conserved among all Alphabaculoviruses (Table 2).
Ac79: ac79, unknown function
The ac79 gene encodes a hypothetical protein (12.2 kDa, 104 aa) with a conserved endonuclease GIYYIG catalytic domain. This domain shows similarity with bacteriophage T4 segA-E genes and with group Ⅰ introns of fungi (245). The GIY-YIG motif belongs to the homing endonuclease family, members of which catalyze double-stranded breaks in DNA to facilitate homing of introns (235). Orthologs of ac79 are found in several Alphabaculoviruses (Table 2), but its function in baculovirus biology remains enigmatic.
Ac80: gp41, tegument protein
The gene gp41 is expressed as a late gene with transcripts starting within two consensus late transcription start sites (TAAG), located immediately upstream of the first ATG codon (276). The 41 kDa prote