o 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 majority of Alphabaculoviruses (Table 2).
Ac30: ac30, unknown function
The ac30 gene codes for a protein (54.7 kDa, 463 aa) with unknown function. Transcripts are present during viral infection (287). Homologous are present in some but not all Alpha-and Betabaculoviruses (Table 2 and Table 3).
Ac31: sod, superoxide dismutase
Transcription of the sod gene results in two RNAs of 1.4 and 1.5 kb which are detectable at 24-48 h and 12-48 h p.i., respectively (263). The encoded superoxide dismutase (16.2 kDa, 151 aa) is not essential for virus replication in cell culture or in larvae (263). Homologs are found in almost every Alphabaculovirus and in a few Betabaculoviruses (Table 2 and Table 3). The sod gene, therefore, may have an important function in the Alphabaculovirus' life cycle (109).
Ac32: fgf, fibroblast growth factor
The fgf gene encodes a fibroblast growth factor homolog (FGF; 20.6 kDa, 181 aa) and homologs are only present in baculoviruses that infect lepidopteran insects (Alpha-and Betabaculoviruses) (48). FGFs have an important role in angiogenesis, cell proliferation, differentiation, and cell migration (110). AcMNPV FGF is also functional in cell culture, as it is secreted and able to enhance cell migration (48). An fgf deletion mutant showed no differences in production of infectious BV nor in DNA replication in Sf21 cells nor did the mutant have a replication advantage (50). In insect larvae of S. frugiperda and T. ni death was delayed compared to the wild type virus with oral feeding, but not with intrahemocoelic injection (49). These results suggest that FGF plays a role in the systemic spread of the virus from the midgut (49).
Ac33: hisp, histidinol-phosphatase
The gene hisp codes for a protein (20.8 kDa, 182 aa) with putative histidinol-phosphatase activity due to the presence of a conserved haloacid dehalogenaselike hydrolase domain. The function of histidinolphosphatase is to catalyze the dephosphorylation of L-histidinol phosphate and such enzymes have been characterized mainly in prokaryotes (211).