38 (ac153) respectively, is needed to accumulate G-actin into the nucleus of Tn-368 cells (202). The expression of ac4, ie-1, and pe38 starts before the expression of ac102 or he65. The gene ac4 codes for a protein of 17.6 kDa (83 aa.) which has not been characterized thoroughly, but it has enhancer activities for cellular and viral promoters (162).
Ac5: ac5, enhancer
In BmNPV, a region upstream of the polyhedrin promoter corresponding to the 5'-ends of ac4 and ac5 of AcMNPV was shown to have enhancer capabilities (1). This enhancer activity was confirmed as the homologous region in AcMNPV resulted in increased promoter activity in luciferase-assays in combination with several full or minimal promoters: hsp70, CMVm and p35 minimal promoter in insect cells (162). In AcMNPV ac5 encodes a hypothetical protein (12.4 kDa, 109 aa), however no transcripts have been detected (287).
Ac6: lef-2, late expression factor 2
The lef-2 gene codes for late expression factor-2 (LEF-2), (23.9 kDa, 210 aa). This protein is essential for the expression from vp39 and polh promoters (216). In addition, LEF-2 as well as five other gene products (IE-1, LEF-1 LEF-3, DNA polymerase, and helicase) are required for replication of plasmid DNA containing an AcMNPV origin of replication (133). Protein-protein interaction between LEF-1 and LEF-2 is essential for this DNA replication (61) and LEF-2 binds to DNA (187). A point mutation changing an aspartic acid into an asparagine residue at amino acid 178, showed no difference in plasmid replication between mutant and wild type virus infections but showed deficiency in very late gene expression (184). Lef-2 is a baculovirus core gene.
Ac7: orf603, ORF603 peptide
The orf603 gene encodes a hitherto uncharacterized protein of 23.6 kDa (201 aa). Partial deletion of the orf603 gene did not affect BV yield in cell culture nor the dose to kill insects (72). However, a truncation of ORF603 decreased the time to death in S. frugiperda larvae (224).
Ac8: polh, major occlusion body protein
The polh gene encodes the 28.6 kDa polyhedrin protein (245 aa), which is the major component of OBs in NPVs. It was the first baculovirus gene to be characterised (105). AcMNPV polyhedrin has a mosaic structure, which makes it unsuitable for phylogenetic analysis (117). polh is the most conserved gene in baculoviruses. The gene is described very late after infection from a canonical TAAG motif. The function of the polyhedra is to protect and spread the virus outside the host. Upon ingestion by the host, the polyhedra dissociate due to the alkaline environment of the midgut and release the virions (129). The gene is not essential for virus replication in cell culture and its promoter is used extensively to drive the expression of foreign genes. For a more detailed review see (236).
Ac9: orf1629, P78/83 capsid protein
The orf1629 gene codes for the essential P78/83 structural protein of BVs and ODVs (226). The protein with a calculated mass of 60.7 kDa (543 aa) has a phosphorylated and a non-phosphorylated isoform, and is present at one end of the mature nucleocapsid (272). P78/83 resembles Wiscott-Aldrich Syndrome proteins (WASP) and is, together with the host protein complex ARP2/3, responsible for actin polymerization in the nucleus of infected cells (74, 175). By deleting part of orf1629 from the AcMNPV genome, a new method was developed to obtain recombinant baculoviruses by dominant selection with almost 100% recombination efficiency (130).
Ac10: pk-1, protein kinase
The protein product of this gene, PK-1 (32.0 kDa, 272 aa), has high similarity to serine-threonine protein kinases and phosphorylates histone H1 in rabbit reticulocyte lysates (233). The gene is expressed from the beginning of the late throughout the very late phase of the viral infection (233). PK-1 is required for transcription of the very late polh gene, presumably through phosphorylation of LEF-8 (ac50), which is required in the (very) late transcription complex (190, 191). PK-1 interacts with PKIP (ac24), which stimulates PK-1 activity (62).
Ac11: ac11, unkno