8: ac38, ADP-ribose pyrophosphatase
The Ac38 protein (25.3 kDa, 216 aa) has homology with proteins in the Nudix (nucleotide diphosphate X) superfamily of pyrophosphatases and contains the conserved Nudix motif: GX5EX7REUXEEX2U (U: I, L or V, and X: any amino acid). Within this superfamily, the Ac38 protein shows the closest phylogenetic relationship with ADP-ribose pyrophosphatases (ADPRases). Recombinant Ac38 indeed has in vitro ADPRase activity (70). Transcripts of ac38 are detectable from 2 h p.i. and the level increases during the late stage of infection. Deletion of ac38 decreases the yield of BV to less than 1% of the wild type virus (70). So far, the gene is conserved in all Alpha-and Betabaculoviruses (Table 2 and Table 3).
Ac39: p43, ODV protein of unknown function
The 43.5 kDa protein P43 (363 aa) encoded by the gene ac39, is present in the proteome of ODVs (20). No putative conserved domains have been detected and its function other than being an ODV protein is still enigmatic. Homologs are present in seven NPV genomes.
Ac40: p47, transcription regulator
The ac40 gene product has a molecular mass of 47.5 kDa (P47;401 aa) and belongs to the group of factors required for late gene expression (262). Moreover, the gene p47 together with three other genes ac50, ac62 and ac90 -coding for lef-8, lef-9 and lef-4, respectively -form a RNA polymerase complex that transcribes late and very late viral genes (88), while early genes are transcribed by the host RNA polymerase Ⅱ (106). P47 directly binds to all other subunits of the late viral RNA complex, as well as to itself, and P47 is required for the association of LEF-4 with LEF-8 (44). Ac40 is a baculovirus core gene.
Ac41: lef-12, late expression factor 12
Ac41 encodes late expression factor 12, LEF-12 (21.1 kDa, 181 aa), which stimulates late gene expression in transient assays in a cell type specific manner (167). In a virus context, lef-12 is neither essential for virus replication nor for expression of late genes, but it has a stimulatory affect on late gene expression levels and virus yield (85). Lef-12 expression depends on DNA replication and the mRNA is synthesized by 12 h p.i. LEF-12 protein is first detected 18 h p.i. and peaks at 24 to 36 h p.i., (85). The expression of lef-12 is diminished when it is not present in cis with sequences present within the nearby ORF ac45 (149).
Ac42: gta, global transactivator-like protein
The ac42 gene encodes a putative 59.1 kDa (506 aa) global transactivator-like protein (GTA) and homologs are found only in group Ⅰ NPVs (Table 2). Baculovirus GTA proteins contain conserved regions belonging to the SNF2-N terminal domain and the helicase C-terminal domain superfamilies (142). The presence of these domains suggests a role in ATP-dependent DNA unwinding. In Choristoneura fumiferana (Cf) MNPV, the region upstream of the gta gene has an early CAGT promoter motif and a transcript is detectable at 6 h p.i. (142). Baculovirus consensus promoter motifs are absent in the AcMNPV gta upstream sequence.
Ac43: ac43, unknown function
Ac44: ac44, zinc finger protein with unknown function
Ac44 is a putative early gene encoding a 15.0 kDa (131 aa) protein with a zinc finger motif (9), suggesting a role in DNA binding. Transcripts from this ORF have been demonstrated by microarray analysis (287). The homolog in BmNPV (Bm35) contains a region rich in C and H residues, resembling RING-finger motifs. Such motifs are found in ubiquitin-ligase (E3), but Bm35 may have a different function since it tested negative for E3 activity (111).
Ac45: ac45, unknown function
Ac45 encodes a predicted protein of 22.7 kDa (192 aa) with unknown function. The presence of the ac45 ORF stimulates expression of lef-12 (ac41) (149). This stimulatory effect is only observed when provided in cis, suggesting that the ac45 region acts either as an enhancer of lef-12 transcription or produces an as yet unobserved protein as a result of mRNA splicing, combining ac45 and lef-12 sequences (149).
Ac46: odv-e66, occlusion-derived virus envelope protein
ODV-E66 (predicted mass 