Ro)MNPV the ac58 and ac59 orthologs are fused into one ORF of 172 codons (92). This is also the case in e.g. BmNPV. Partial resequencing of the AcMNPV C6 strain confirmed that ac58 and ac59 are in fact one ORF (92).Ac58/59 encodes a 20.3 kDa (172 aa) protein. Ac58/59 specific peptides were found within or associated with the ODVs by proteomic analysis (20). Ac58/59 belongs to the ChaB superfamily, originally known in E. coli in combination with ChaA, a cation transporter. The role of ChaB proteins in baculoviruses is unclear.
Ac60: ac60, unknown function
Ac60 was predicted by sequence analysis to potentially encode a 10.1 kDa (87 aa) protein (9). Transcript levels from this ORF were reduced by 72% in a pp31 (ac36) deletion mutant (287). As in the Ac58/59 protein, Ac60 contains a ChaB superfamily domain.
Ac61: fp/25k, FP protein
FP25K (25.2 kDa, 214 aa) is a structural protein of BVs and ODVs (16). Ac61 mutants show a reduction in polyhedrin transcripts, but have wild type p10 expression levels (93). Mutations in FP25K also reduce ODV-e66 expression and transport of ODV-E66 protein to the nucleus is inhibited (16). A more general role has been proposed for FP25K in targeting and intracellular transport of viral proteins during infection (16). In BmNPV it has been shown that FP25K is required for maintaining transcriptional regulation and efficient secretion of V-CATH and maintaining a steady-state level expression during secretion (125).
During serial passage of AcMNPV in cultured insect cells spontaneous mutants occur having the "few polyhedral" (FP) phenotype. This is the result of frequent transposon insertions in this area (10). These mutants have typical characteristics (94), including a reduced number of occlusion bodies, no envelopment of nucleocapsids within the nucleus and enhanced BV production.
Ac62: lef-9, late expression factor 9
The protein LEF-9 has a molecular mass of 59.3 kDa (516 aa) and is required for late and very late gene expression (168). LEF-9 contains RNA polymerase motifs and is an essential subunit of the RNA polymerase complex encoded by AcMNPV. Mutations in the conserved RNA polymerase motif showed the requirement of conserved asparagine residues (44) LEF-9 and LEF-8 interact directly (44) (see also ac40).
Ac63: ac63, unknown function
The Ac63 protein has a predicted mass of 18.5 kDa (155 aa) and does not contain any known conserved domains. Homologs are present in several Alphabaculoviruses (Table 2).
Ac64: gp37, spindle body protein or GP37
ORF ac63 encodes a glycoprotein with a predicted molecular mass of 34.8 kDa (P34.8, 302 aa) and is a homolog of the OpMNPV spindlin, which in that virus is a component of OBs (80). Baculovirus GP37 proteins are homologous to entomopoxvirus fusolins (221). Disrupting the gene in AcMNPV showed that the gene is not essential for virus replication nor affects virulence or speed of kill (34).
Ac65: dnapol, DNA polymerase
The ac65 gene codes for DNA polymerase (114.3 kDa, 984 aa) and is conserved among all baculoviruses. It is disputable whether it is essential for DNA replication in transient replication assays (133) or only stimulatory (169). Vanarsdall et al. (269) have shown using quantitative PCR (qPCR) that an AcMNPV-bacmid lacking dnapol cannot replicate its DNA in Sf9 cells.
Ac66: ac66, desmoplakin-like (ODV protein of unknown function)
The gene ac66 encodes a protein of 94.0 kDa (808 aa) and contains two conserved domains: a viral desmoplakin N-terminal domain and a CorA-like Mg2+-transporter region, respectively. Desmoplakin is the major component of desmosomes (253), which have a strong adhesive nature. They are involved in intercellular adhesion and participate in cell proliferation, differentiation and morphology (69). The CorA family consists of a group of membrane transporters of metal ions, abundant in prokaryotes, which can also be found in humans and yeast (196). The protein has been found in ODV nucleocapsids, but the exact localization is unknown (20). An ac66-null mutation resulted in depleted BV production due to inefficient transport of 