des 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, unknown function
The ac11 gene encodes a hypothetical protein with a predicted mass of 40.1 kDa (340 aa). Homologs found in many Alphabaculoviruses (Table 2) together form the DUF1386 family (176), but no particular motifs point towards a specific function.
Ac12: ac12, unknown function
This ORF encodes a hypothetical protein of 25.4 kDa (217 aa) with unknown function (9). The gene is not conserved among the Alphabaculoviruses; only in the related virus Rachoplusia ou (Ro)MNPV and in Lymantria dispar (Ld)MNPV homologous genes can be found. In the former the homologous gene is 25 codons shorter than in AcMNPV (92). Microarray analysis revealed transcripts of the gene, but its function remains unknown (287).
Ac13: ac13, unknown function
Ac13 codes for a hypothetical protein with a predicted mass of 38.7 kDa (327 aa). Homologs are conserved among all Alphabaculoviruses and are present in a few granuloviruses (Table 2 and Table 3). Transcripts were found by microarray analysis (287), but no function was assigned.
Ac14: lef-1, late expression factor 1
The gene product LEF-1 with a calculated mass of a 30.8 kDa (266 aa) is essential for DNA replication (133) and forms a complex with LEF-2 (ac6) (61). This interaction is required as non-interacting mutants of LEF-1 and LEF-2 do not promote transient DNA replication (61). LEF-1 contains a primase-like motif (61) and its primase activity was confirmed (187) based on the oligonucleotide synthesis on a poly (dT) template, which then allowed initiation of DNA synthesis by an exogenous DNA polymerase (Klenow enzyme). Lef-1 is a baculovirus core gene.
Ac15: egt, ecdysteroid UDP-glucosyl transferase
The egt gene encodes the enzyme ecdysteroid UDP-glucosyl transferase (EGT) (23.6 kDa, 201 aa). The gene is lost in some baculovirus lineages (100). This enzyme prevents insect molting by inactivating ecdysteroid hormones through transfer of glucosyl groups to these hormones (199). The presence of EGT during infection leads the development of larger insects, a longer time to death and a hi