ion structure, DNA replication, transcription and auxiliary functions. Auxiliary genes are those that are not necessary for virus replication but give replication advantages for the virus at the level of the cell, the organism or the ecosystem (197).
In Table 2 and Table 3, AcMNPV gene orthologs are indicated for the 48 baculoviruses that have been completely sequenced (December 2008). The numbers correspond to their respective ORF number in the particular virus. Homologous genes have been found using Basic Local Alignment Tool (6) for proteins available through the website http://blast.ncbi.nlm.nih.gov/ with the following search set: non-redundant protein sequence database; organism: dsDNA viruses, no RNA stage; blast-p algorithm. Baculoviruses have a common set of 30 genes and these genes are designated as the baculovirus core genes (178, 179). Two Ac-MNPV genes have homologs in all baculoviruses except for the Deltabaculoviruses (ac25 and ac145), one AcMNPV gene has a homolog in all, except Gammabaculoviruses (ac23), twenty in all Alpha-and Betabaculoviruses and sixteen additional genes have homologs in all sequenced Alphabaculoviruses (Table 2 and Table 3).
Ac1: ptp/bvp, protein tyrosine phosphatase or baculovirus phosphatase
This ORF encodes a protein (19.3 kDa; 168 aa) with a chimerical character as it has the characteristics of a protein tyrosine phosphatase (PTP), but it also has RNA-tri/diphosphatase activity (255). The preferred substrate for PTP is RNA and it crystallizes in a metazoan RNA capping enzyme fashion (27). Later it was renamed to baculovirus phosphatase (BVP), which is a protein only produced by group Ⅰ NPVs. The AcMNPV ptp/bvp gene appears to be associated with the wandering behaviour of infected larvae (107), similarly to the closely related Bombyx mori (Bm) NPV ptp gene (122). RNA-triphosphatase activity is also encoded by the AcMNPV lef-4 gene (ac90), which in addition encodes guanyltransferase activity (154).
Ac2: bro, baculovirus repeated ORF
This gene belongs to the baculovirus repeated ORF (bro) family, which has members in many other baculoviruses either as a single gene or in multiple copies. A similar gene is also present in entomopoxvirus (3, 11). The AcMNPV bro gene is present as a single copy and encodes a protein with a predicted mass of 37.8 kDa (328 aa) with unclear function. Disruption of the bro gene has no effect on virus replication in cultured cells or on the lethal dose in insect larvae when injected as BV or per os with ODV. However, disruption of the N-terminal part of the BRO protein reduced the number of OBs (15). In contrast to Ac-MNPV, BmNPV contains five bro genes, bro-a till bro-e. The BmNPV bro-d gene is essential for virus replication in cell culture and bro-a and bro-c genes can complement each other (124). However, the absence of bro genes in several baculoviruses suggests that the requirement for bro genes may depend on the host species (15). In BmNPV, the BRO proteins reside in the nucleus until 4 h post infection (p.i.). After that time point, the proteins are found in both cytoplasm and nucleus (123). Furthermore, mutation in the leucine-rich N-terminal part of the protein results in accumulation of proteins, which suggest that this region serves as a CRM1-dependent nuclear export signal (123).
Ac3: ctl, conotoxin-like peptide
The ctl gene encodes a conotoxin-like peptide, which has a molecular mass of 5.6 kDa (53 aa). Conotoxins are neurotoxins that are present in the venom of marine snails, belonging to the genus Conus (257). Ω-conotoxins block specific types of Ca2+-channels in neurons (180), while another sub-class of conotoxins have a behavioural and anticonvulsant effect in DBA/2 mice (114). Infection with a mutant AcMNPV virus – with either a disruption or a null mutant of the gene – was not significantly different in infectivity in Sf21 cells or in virulence S. frugiperda larvae (57).
Ac4: ac4, putative enhancer activity
ORF 4 of AcMNPV is an early gene and together with five other early genes of AcMNPV, ac102, he65 (ac105), ie-1 (ac147), ac152, and pe