nucleocapsids from the nucleus to the cytoplasm. However, ac66 is not required for the formation of the nucleocapsids, but appears to be involved in pre-occluded virion and occlusion body formation (126).
Ac67: lef-3, late expression factor 3
The lef-3 gene is essential for DNA replication in transient replication assays (133). The 44.6 kDa (385 aa) LEF-3 protein binds to ssDNA (90). LEF-3 forms, together with P143 (helicase; see ac95) and IE-1 (see ac147), complexes with viral chromatin in infected cells (112). It has been proposed that LEF-3 interacts with P143 to stabilize the formed ssDNA after unwinding by the P143 helicase (112). LEF-3 also mediates nuclear localization of P143 (284) due to a nuclear localization signal domain which is required for interaction between LEF-3 and P143 (8).
Ac68: ac68, unknown function
All baculovirus genomes sequenced to date carry a homolog of the AcMNPV ac68 gene (Table 2 and Table 3), suggesting that it performs an important role in baculovirus biology. The conserved sequence is assigned as DUF708 domain, with unknown function (176). Ac68 is transcribed from 3 to 96 h p.i. and the gene product (22.3 kDa, 192 aa) was detected from 36 to 96 h p.i. (148). Deletion of ac68 did not affect production of infectious BVs, nucleocapsid or OB formation, nor did deletion of ac68 change the time to kill in vivo (148).
Ac69: mtase1, MTase1
Ac69 is a late gene (283) and its 30.4 kDa (262 aa) product stimulates late gene expression in vitro (149). The protein is homologous to E. coli FtsJ (148), an RNA methyltransferase and also has an S-adenosylmethionine (AdoMet)-methyltransferase domain. The protein binds AdoMet in vitro and has (nucleoside 2′-O)-methyltransferase activity, allowing coupling of methyl groups to RNA (283). Disruption of the ac69 gene does not affect virus replication in single-step growth curves (283), but the effect in vivo has not been analyzed.
Ac70: hcf-1, host cell-specific factor 1
The gene hcf-1 encodes a 34.4 kDa (290 aa) protein involved in the expression of late and very late gene promoters. HCF-1 is absolutely required for virus replication and late gene expression in TN-368 cells, and its absence is accompanied by a block in cellular and viral protein synthesis (170). In T. ni larvae a hcf-1 mutant, shows a reduced speed of kill. In Sf21 cells and in S. frugiperda larvae replication of hcf-1 mutants is not different from that of the wild type virus, hence the name host cell-specific factor (170).
Ac71: iap-2, apoptosis inhibitor
The gene iap-2 encodes a putative apoptosis inhibitor (28.6 kDa, 249 aa). It contains the conserved RING-finger like-motifs present in all iap genes, but not a BIR repeat region (79). Deletion of either iap-1 (ac27) or iap-2, or the simultaneous deletion of both genes did not have an effect on the replication of the virus in Sf21 cells (79). Whether it has a role in inhibiting apoptosis remains unclear. In other NPVs IAPs have been shown to inhibit apoptosis (36).
Ac72: unknown function
Ac73: ac73, unknown function
Homologs of the predicted gene ac73 (11.5 kDa, 99 aa protein) are present in genomes of several other members of the genus Alphabaculovirus (Table 2). Information about the (putative) function of ac73 in the viral life cycle is not available, but transcripts are made (287).
Ac74: ac74, unknown function
Ac75: ac75, unknown function
Homologs of ac75 can only be found in genomes of Alphabaculoviruses (Table 2). The predicted gene product has a molecular mass of 15.5 kDa (133 aa) and transcripts have been detected with micro-arrays (287). There is no publication about the role of ac75 in baculovirus biology.
Ac76; ac76, unknown function
Homologs of ac76 can be found in genomes of all Alphabaculoviruses (Table 2). The predicted gene is transcribed (287) and encodes a hypothetical protein of 9.4 kDa (84 aa). No data about the role of ac76 in the baculovirus replication cycle are available.
Ac77: vlf-1, very late expression factor 1
Ac77 or the vlf-1 gene is involved in the expression of the very late genes p10 and polh (183, 288). The g