anscript 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 is not affected (160). Therefore, the encoded 17.0 kDa (139 aa) protein is most likely involved in nucleocapsid assembly and may have a role in condensation or packaging of viral DNA. Its crucial role is reflected by the presence of ac53 orthologs in all sequenced lepidopteran and hymenopteran baculovirus genomes (Table 2 and Table 3). The homologous protein encoded by BmNPV (Bm42) is present in BVs, but is absent in ODVs (2).
Ac53a: lef-10, late expression factor 10
The gene lef-10 belongs to the group of 18 genes that support late gene expression (262). The exact function is unclear, but the LEF-10 protein (8.6 kDa, 78 aa) might be involved in promoter recognition, stabilization of late transcripts or could be associated with the virus-induced RNA polymerase complex (169). The gene has been classified as an auxiliary factor in the transcription process (97).
Ac54: vp1054, VP1054 viral capsid-associated protein
The vp1054 region produces multicistronic mRNAs from early to very late times after infection (209). VP1054 is a 42.1 kDa (365 aa) structural protein present in both BVs and ODVs required for nucleocapsid formation (209). VP1054 interacts with the 38K protein (ac98) in infected cells (281) and is encoded by a baculovirus core gene
Ac55: ac55, unknown function
Ac55 is an early gene for a hitherto unidentified 8.2 kDa (73 aa) protein without known domains. A mRNA from this ORF has been demonstrated (287).
Ac56: ac56, unknown function
Ac56 encodes a small putative protein of 9.9 kDa (84 aa) protein for which no conserved domains have been found. A transcript from this ORF was found by microarray analysis (287).
Ac57: ac57, unknown function
Ac57 is a putative early gene encoding a 19.0 kDa.(161 aa) protein. Microarray studies revealed a transcript from this ORF (287). The Ac57 protein and its orthologs in other Alphabaculoviruses form the DUF918 superfamily (176), but this gives no further clues concerning its function.
Ac58/59: ac58/59, ODV protein of unknown function:
In the closely related Rachoplusia ou (