ne 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 79.1 kDa, 704 aa) is an integral ODV envelope protein that like ODV-E25 (ac94), is N-terminally anchored in the envelope (104, 239). ODV-E66 is not required for BV production (240). The N-terminal region of AcMNPV ODV-E66 enables trafficking of marker proteins to intranuclear membranes and the ODV envelope (104). This region has two features: (ⅰ) a hydrophobic sequence of 18 aa and (ⅱ) positively charged amino acids close to the C-terminal end of the hydrophobic sequence. The latter may comprise a sorting motif for selection of proteins to the inner nuclear membrane (21).
Ac47: ets, unknown function
The 88-codon ets ORF has the ability to encode a 10.5 kDa protein (88 aa), and shows sequence homology to a small part of the vesicular stomatitis virus RNA polymerase gene (similarity 50% for a 250 bp region) (42). The ets gene represents the smallest ORF in a polycistronic unit in the EcoRI-T fragment (hence its name). The other ORFS in this unit are with ORFs ac48 or etm, the medium-sized ORF, and ac49 (etl/pcl) for the largest ORF in the unit), as further described below in the context of ac49.
Ac48: etm, unknown function
The gene etm encodes a putative 12.9 kDa (113 aa) hydrophobic protein with unknown function (42). It is part of a polycistronic unit with ORFs ac48 and ac49, as outlined in detail under ac49.
Ac49: pcna, proliferating cell nuclear antigen
The pcna gene (previously etl) encodes a 28.6 kDa protein (256 aa) with 42% amino acid identity to rat proliferating cell nuclear antigen (198). The gene pcna forms the largest ORF in a putative polycistronic unit comprising pcna, etm (ac48) and ets (ac47). The largest and most predominant transcript from this region is an early 1.7 kb poly (A)+ RNA, which contains each of the three tandem, non-overlapping ORFs. Smaller (0.5 kb) heterogeneous transcripts are also observed from the cistron, corresponding to ets (ac47). Both the 1.7 and 0.5 kb transcripts are present at 4 h p.i.. Whilst the 1.7 kb transcripts are shut off at 12 h p.i., the levels of the smaller tr