, 55 aa), very basic (pI=12), protamine-like protein named: Basic Protein or P6.9. The positively charged arginine residues of P6.9 interact with the viral DNA genome to mediate DNA condensation in the nucleocapsid (127). In infected cells P6.9 is phosphorylated, but in nucleocapsid assembly this phosphorylation is inhibited by the presence of Zn2+(68). A model for this packaging has been proposed: during packaging of viral DNA, P6.9 is dephosphorylated by cellular phosphatases followed by DNA condensation. Phosphorylation of P6.9 by a capsid-associated kinase results in unpackaging of the nucleocapsid upon entry into cells, allowing the onset of the infection cycle (68). P6.9 is a baculovirus core gene.
Ac101: p40, BV/ODV-C42
The gene ac101 is transcribed at the late stage of infection. It encodes a 42 kDa protein (41.5 kDa predicted molecular mass, 361 aa), which is a component of the nucleocapsid of both BVs and ODVs (18). There is strong evidence that ODV-C42 is capable of direct interaction with the WASP-like protein P78/ 83 (ac9) and ODV-EC27 (ac144) (18). ODV-C42 probably binds to the viral protein P78/83 in the cytoplasm to form a protein complex, which then migrates to the nucleus during AcMNPV infection due to the nuclear localization signal in ODV-C42 (274). A mutant virus lacking ac101 is not able to propagate in cell culture as no mature nucleocapsids are formed, however, viral genome replication was not affected (270). Direct interaction between BV/ODV-C42 and a leucine zipper domain of EXON0 (ac141) enables egress of nucleocapsids from the nucleus to cytoplasm during the late phase of infection (64). Homologs of the gene ac101 are present in all sequenced baculovi-ruses except CuniNPV (249) (Table 2 and Table 3).
Ac102: p12, transport of G-actin
The transcription of the gene coding for the 12-kDa protein (13.3 kDa predicted, 122 aa) initiates from the consensus baculovirus late transcription start site (ATAAG) (166). Attempts to prepare a p12-mutant were not successful, suggesting that the gene is essential for virus replication in cell culture (166). Together with the products of the genes ie-1 (ac147), pe38 (ac153), he65 (ac105), ac4, and ac152, P12 is involved in transport of G-actin into the nucleus during baculovirus infection (202).
Ac103: p48, unknown function
The 5' end of the p48 transcript maps to consensus baculovirus late transcription start sites (ATAAG) (166). Attempts to prepare p48 mutant viruses were not successful suggesting that the gene is essential for virus replication in cell culture (166). More recently, detailed analysis of a p48 deletion mutant confirmed that this gene is essential for BV production and ODV envelopment (290). Homologs of ac103 can be found in the genomes of all Alpha-, Beta-and Gammabaculoviruses (Table 2 and Table 3).
Ac104: vp80, capsid-associated protein VP80
A late 2.1 kb transcript was mapped to ac104 which encodes a 79.9 kDa protein (691 aa). VP80 is a structural capsid-associated protein as confirmed with anti-BV sera (164). VP80 interacts with the viral protein, 38K (see ac98) (281). In BmNPV, VP80 is essential for BV production and nucleocapsid maturation. The BmNPV vp80 could not functionally be replaced by AcMNPV vp80 (256). In the case of Choristoneura fumiferana (Cf) MNPV, the VP80 protein appears as a 82 kDa protein in samples from ODVs and as an 72/82 kDa doublet from BVs (151). Homologs of the vp80 gene are only found in Alphabaculoviruses (Table 2).
Ac105: he65, HE65 protein
The designation he65 stems from the size of the predicted protein (65.6 kDa, 553 aa) and the genomic location of this ORF, being flanked by an EcoRI site and the hr4 left region. He65 is a delayed early gene and mRNA is detectable from 2 h p.i.. Transcript levels remain stable into the late phases of infection (12). HE65, together with Ac102, mediates nuclear localization of monomeric G-actin, a process promoting nuclear F-actin formation, which is required for progeny virus production (202). Localization of G-actin within the nucleus is a temporally regulated process. Transac