n 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, unknown function
The gene ac154 encodes a protein (calculated mass 9.4 kDa, 81 aa) with unknown function. Transcripts of this gene have been identified (287). Only four homologs are present in other Alphabaculoviruses (Table 2).
The research towards elucidating the function of AcMNPV genes started in the early 1980s with the assignment of polyhedrin and p10, but was enhanced by the publication of the complete genome sequence in 1994 showing originally 154 ORFs (9) to which ac53a (lef-10) was added later. Partial re-sequencing of the AcMNPV C6 strain at a later date, demonstrated that four ORF pairs were actually fused (ac20/21, ac58/59, ac106/107, ac112/113), bringing the total to 151 ORFs (92). For many ORFs, we had little or no idea about their putative function. Overtime, many ORFs were assigned (see Table 1), mainly associated with transcription, DNA replication, virion structure and pathogenesis. Nevertheless, as of January 2009, 73 ORFs still remain with an unknown function. The most striking ORFs were those involved in the inhibition of apoptosis (p35) and in abrogation of the molt (egt). These observations provoked resonance far beyond baculovirology.
Functional studies in other, closely-related baculovi-ruses are sometimes useful to indicate which role an encoded AcMNPV protein might have. However, discrepancies have been found, which may reflect intrinsic differences in the viral protein under study. The discrepancies may also reflect dissimilarities in the presence or absence of other baculovirus gene products or in the interplay with host factors.
Many of the AcMNPV ORFs with unknown function encode relatively small proteins, sometimes with homologs in only a few baculoviruses, and therefore may not be functional or may not have a very crucial role. Others with unrevealed function, though, belong to the baculovirus core genes at the family level, or are represented in a whole genus, and must play key roles in baculovirus biology. Some of these genes may very well play a role in baculovirus ecology rathe