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 transcript persist until late after infection (42). Cellular PCNAs colocalize with viral DNA replication sites and complement viral PCNA in pcna-defective viruses (113). In transient replication assays, PCNA did not stimulate DNA replication (133, 149), nor is it essential for virus replication, at least in proliferating cell cultures (198).
Ac50: lef-8, late expression factor 8
The gene lef-8 encodes the late expression factor 8 (101.8 kDa, 876 aa), which is the largest subunit of the RNA polymerase complex (see ac40). LEF-8 harbors a conserved sequence motif GXKX4HGQ/ NKG found in DNA-directed RNA polymerases (217). LEF-8 directly associates with LEF-9 (ac62), the other protein with RNA polymerase motifs and with P47 (ac40) (44). LEF-8, like all other RNA poly-merase subunits, is encoded by a baculovirus core gene.
Ac51: ac51, BJDP (unknown function)
The early gene ac51 encodes a predicted (37.5 kDa, 318 aa) protein. A transcript has been demonstrated by microarray analysis, however its function remains unknown (287). The ortholog splt39 from SpltNPV is a late gene and encodes a protein described as baculovirus J domain protein (BJDP). It has a predicted coiled-coil domain and RNA recognition motif, and is present in both ODVs and BVs (273). AcMNPV ODVs do not contain detectable amounts of Ac51 protein (20), which appears to be in line with the early promoter motifs of this ORF.
Ac52: ac52, unknown function
The gene ac52 is putatively an early gene for a 14.9 kDa (123 aa) protein. A detectable mRNA transcript from this ORF was found in microarray analysis (287).
Ac53: ac53, unknown function
Ac53 is located in a gene cluster of five ORFs (ac53, lef-10 (ac53a), vp1054 (ac54), ac55 and ac56), which all have the same clock-wise orientation. This cluster is conserved in many group Ⅰ NPVs (160). In BmNPV many overlapping, 3'co-terminal mRNAs are transcribed from this region (2). Deletion of ac53 affects BV formation. Tubular, incomplete capsid-like structures lacking nucleic acids are present, although DNA replication 