ene 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 protein (predicted molecular mass 45.4 kDa, 409 aa) has O-glycosidically linked N-acetylglucosamine (GlcNAc) residues and is present between the envelope membrane and the nucleocapsids of ODVs (277). A thermosensitive (ts) gp41 mutant causes single-cell-infections, which progress through the very late phase including the formation of OBs. However, infection does not spread to neighboring cells (210), indicating that BV production is affected in the ts-mutant, although GP41 is only found in ODVs (277). Ac80 is conserved in all baculovirus genomes.
Ac81: ac81, unknown function
The ac81 gene is highly conserved and belongs to the baculovirus core genes. The gene product has a predicted mass of 26.9 kDa (238 aa) and the homologous protein in BmNPV (Bm67) is detected neither in BVs nor ODVs. Immunofluoresence analysis showed that the Bm67 protein is present in the cytoplasm and interacts with the host protein actin A3 (31). Bm67 is required for the production of infectious BV (71). Bm67 mutations negatively affect viral DNA synthesis and the stability of nascent viral DNA. Nucleocapsids with a wild type morphology are hardly found and nucleocapsids are only occasionally exported to the cytoplasm. The envelopment of nucleocapsids is also abnormal with these Bm67 mutants (71).
Ac82: tlp, telokin-like protein-20
The gene ac82 encodes a protein with a predicted molecular mass of 20 kDa (19.8 kDa, 180 aa). In Western blot analysis it shows a size of 28 kDa and reacts with an antibody specific against the smooth muscle protein telokin, hence the name telokin-like protein or TLP (232). However, no amino acid sequence similarity exists between TLP-20 and telokin. 3-D structure analysis of TLP-20 showed a seven-stranded antiparallel β-barrel flanked on the basis by two additional β-strands and on the top by an α-helix. As such, TLP-20 does not resemble the structure of any other known protein (101).
Ac83: p95, viral capsid associated protein, VP91
The gene p95 encodes a protein (96.2 kDa, 847 aa), with two conserved domains: a vira