tein belonging to the baculovirus core genes and is often used in baculovirus phylogeny.
Ac23: ac23, copia-like envelope protein
The gene ac23 is a truncated, non-functional homolog of the baculovirus F-protein present in group Ⅱ NPVs of the Alphabaculoviruses and in Beta-, and Deltabaculoviruses. The F-protein homolog or F-like protein Ac23 (79.9 kDa, 690 aa) does not function as fusion protein, as it lacks a functional furin cleavage site, but it may have other functions (219). An AcMNPV-mutant lacking ac23 showed that the gene is not essential for either infection, virus propagation or BV production, but the mutant killed T. ni larvae slower than wild type virus, suggesting that the F-like Ac23 protein is a viral pathogenicity factor in vivo (173).
Ac24: pkip, protein kinase interacting protein
The gene ac24 or pkip is a late gene and encodes a protein kinase-interacting protein (PKIP; 19.2 kDa, 169 aa) (62). PKIP interacts with PK-1 (see ac10) in virus-infected cells and stimulates activity of PK-1 (62). A temperature sensitive pkip mutant showed neither BV production nor VL gene expression, but intracellular nucleocapsids of this mutant structurally resembled those of the wild type AcMNPV (182).
Ac25: dbp, ssDNA-binding protein
Homologs of the dbp gene have been identified in all sequenced baculovirus genomes, except the dipteran CuniNPV (205). DBP (36.6 kDa, 316 aa) is expressed as an early gene product (204), which is essential for the production of viable virions. However, it is not required for synthesis of viral DNA nor for expression of viral genes (231, 267). DBP has a tight association with subnuclear structures and has high affinity for ssDNA. It has both DNA unwinding and renaturation activities and may be involved in the processing of replication intermediates (188).
Ac26: ac26, unknown function
The ac26 gene encodes a protein with a theoretical molecular mass of 14.6 kDa (129 aa) and has a conserved domain with unknown function in the NCBI Conserved Domain Database (CDD) (176). The gene appears to be transcribed (287), but the function remains unclear. The majority of the homologs can be found in Alphabaculoviruses (Table 2).
Ac27: iap-1, inhibitor of apoptosis
The gene iap-1 encodes a protein (33.3 kDa, 286 aa) containing an imperfect 70-amino acid repeat, called a baculovirus IAP repeat (BIR) at the N-terminus and an additional Cys3-His-Cys4(C3HC4) zinc or RING-finger-like motif at the carboxyl-terminus (79). Ac27 was named iap-1 on the basis of homology to the Cydia pomonella (Cp) GV iap gene (43). Expression of iap-1 does not block the induction of apoptosis by AcMNPV p35 (ac135) deletion mutants (36). The gene is transcribed early and late after infection as a part of a bicistronic mRNA, which also includes lef-6 (ac28) sequences (214). Spontaneous deletion in the PstI-I fragment harbouring the iap-1 gene occurs during serial passage of the virus (139). Three spontaneous recombinant viruses with different mutations showed no abnormalities in the rate of replication and the amount of BV and ODV produced in cell culture (181). However, in competition-assays, the mutant lacking iap-1 has a replication advantage over wild type AcMNPV in TN-368, but not in Sf21 cells (181).
Ac28: lef-6, late expression factor 6
Lef-6 is transcribed into a monocistronic mRNA at 9 h p.i. and at 12 h p.i, but lef-6 is transcribed together with iap-1 as a bicistronic mRNA at 12 h p.i. (214). LEF-6 is most abundant between 12 and 24 h p.i. (156). Furthermore, LEF-6 (calculated mass 20.4 kDa, 173 aa) is localized in the nuclei of infected cells (156) and is involved in expression of L and VL genes (214). LEF-6 is not essential for viral reproduction, DNA replication or late transcription in Sf9 cells. However, late gene transcription and the production of BVs were delayed and reduced (156).
Ac29: ac29, unknown function
The gene ac29 encodes a hypothetical protein with calculated mass of 8.6 kDa (71 aa). The gene is transcribed (287), but its function is not described in the literature. Homologous genes are present in the major