cidic activation domain at the N-terminus, a DNA binding domain, and an oligomerization domain at the C-terminus (47, 136). Compared to IE-1, IE-0 has 52 extra N-terminal amino acids. IE-1 is a potent transcriptional transactivator and essential for virus replication (133). A virus lacking either ie-1 or ie-0 could be propagated in cell culture, but a double knock-out is not viable. The ie0-ie1 gene complex is essential for viral infection and is needed to obtain wild type levels of replication, late gene expression and BV and ODV production (243, 197). De novo synthesis of IE-1 leads to virus-induced apoptosis (252). IE-1 also transactivates the expression of the p35 gene, and in that way counteracts its own pro-apoptotic activity (243). Homologs are found in all Alphabaculoviruses (Table 2).
Ac148: odv-e56, occlusion-derived virus envelope protein
Transcription of the gene odv-e56 starts from a late ATAAG promoter and transcripts are detected from 16 to 72 h p.i. (17). ODV-E56 protein (predicted 40.9 kDa, 476 aa) is present in viral-induced intranuclear microvesicles, and consequently is incorporated into ODV envelopes (17). Mutation in the 3x-end of odv- e56 alters its location to the nucleocapsids instead of the ODV envelope, suggesting that an important localization sequence is present in the C-terminus of this protein (17).
Ac149: ac149, unknown function
The ac149 ORF encodes a putative protein of 12.4 kDa (107 aa) with unknown function. Homologs are present in a few related Alphabaculoviruses (Table 2).
Ac150: ac150, unknown function
The gene ac150 encodes an 11.2 kDa (99 aa) protein and is expressed in the late to very late phase of infection. The protein Ac150, is a member of a family containing peritrophin-A-like domains (see also ac145) -common among mucins, peritrophins and chitinases -and the protein contains an integrin-binding motif (143). Deletion of ac150 has no effect on infectivity of the virus for T. ni or H. virescens larvae, but the mutant is less efficient in establishing a primary infection in midgut cells, although the infectivity kinetics are the same as for the wild type virus (291). These results together suggest that ac150 can be considered as a putative per os infection factor (PIF) that mediates, but is not essential for, oral infection (291). This has been confirmed as a deletion of the homologous gene (bm126) in BmNPV shows no difference in BV production and mean lethal dose of OBs. However the median survival time in larvae is delayed (91).
Ac151: ie-2, immediate early transactivator 2
The ie-2 gene encodes the immediate early protein IE-2 (47.0 kDa, 408 aa), which functions as a transactivator of early baculovirus promoters in transient expression assays (26). Other functions of the protein are blocking the progression of the cell cycle in a variety of cell lines (229) and augmenting the replication and stability of reporter plasmids containing hr sequences in the presence of IE-1 and four other AcMNPV gene products (133, 167). Viruses with ie-2 mutations exhibit delays in viral DNA synthesis, late gene expression, BV production, and OB formation in Sf21 cells but not in TN-5B1-4 cells (227).
The gene ac152 encodes a protein of 10.8 kDa (92 aa). The protein Ac152 is involved in nuclear localization of G-actin in TN-368 cells and is a transactivator (directly or indirectly) of both ac102 and he65 genes (202).
The gene product of pe38, the protein PE38 (321 aa), is present during the early phase of infection as a nuclear 38 kDa protein, but during the late phase, it is modulated to or produced as a cytoplasmic 20 kDa protein in a process which is controlled by viral factors (137). PE38 is a protein with RING finger and leucine zipper motifs and is involved in transactivation of viral genes and augmenting viral DNA replication in transient replication assays (133, 137). Furthermore, PE38 is augments IE1-induced apoptosis, but is not able to induce apoptosis when expressed in Sf21 cells alone (228). PE38 is an important factor in viral DNA synthesis and BV production (189).
Ac154: ac154, un