The genome of the Lymantria dispar multinucleocapsid nucleopolyhedrovirus (LdMNPV) was sequenced and analyzed. It is composed of 161,046 bases with a G + C content of 57.5% and contains 163 putative open reading frames (ORFs) of >/=150 nucleotides. Homologs were found to 95 of the 155 genes predicted for the Autographa californica MNPV (AcMNPV) genome. More than 9% of the LdMNPV genome was occupied by 16 repeated genes related to AcMNPV ORF2. Readily identifiable homologs of several genes that have been reported to play important roles in the AcMNPV life cycle are not present; these include ie-2, a transcriptional transactivator, and gp64, a major envelope glycoprotein of the nonoccluded form of the virus. A number of genes lacking in AcMNPV but present in other baculoviruses were identified; these include two viral enhancing factor homologs, a second copy of a conotoxin-like gene, and a dutpase homolog. Although a single gene predicted to encode a large subunit of ribonucleotide reductase was found, two different copies of the small subunit gene were present. In addition, homologs of genes not previously reported for baculoviruses were identified, including a predicted protein with homology to DNA ligases and another that has motifs most closely related to a yeast mitochondrial helicase. Thirteen homologous regions (hrs) containing 54 repeated sequences that include 30-bp imperfect palindromes were identified. The imperfect palindromes are related to those from other baculoviruses.

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The complete genome sequences of a number of diverse members of the Baculoviridae including both nucleopolyhedroviruses (NPVs) and granuloviruses (GVs) revealed that they lack a homolog of GP64, the envelope fusion protein of the budded form of Autographa californica multinucleocapsid NPV (AcMNPV) and its close relatives. Computer-assisted analyses of the genome of one of these viruses, Lymantria dispar MNPV The Baculoviridae are a large family of occluded, rod-shaped viruses with circular, supercoiled, double-stranded DNA genomes of 100 to 180 kb depending on the virus strain. Two baculovirus genera have been described; the nucleopolyhedroviruses (NPVs) (34) have multiple virions present in large polyhedron-shaped occlusion bodies, whereas the granuloviruses (GVs) (42) normally display a single nucleocapsid embedded in a small granular occlusion body. NPVs are characterized by the production of two virion forms, or phenotypes (40). Occlusion-derived virions are found in occlusion bodies and initiate infection in midgut cells upon ingestion by susceptible hosts. In contrast, the budded virus (BV) form is not occluded, is produced early in infection, and spreads the infection within the infected insect prior to occlusion body production. Although the nucleocapsids for the two virion forms appear to have similar polypeptide contents, the compositions and structures of their envelopes appear to be distinct (7). BV infection by both Autographa californica multinucleocapsid NPV (AcMNPV) and Orgyia pseudotsugata MNPV (OpMNPV) has been investigated, and a glycoprotein called GP64 has been found to be associated with the BV form of both these viruses (3, 39, 41). GP64 is expressed both early and late in infection and is transported to and incorporated into the cell membrane. As nucleocapsids bud through the cell membrane and exit the cell, they become enveloped in the GP64-modified cell membrane. GP64 appears to be required for the spread of the infection to other cells and for the virus to exit from an infected cell (23,26,28). BV enters cells via an endocytic pathway, and, upon acidification of the endocytic vesicle, the structure of GP64 is altered and fusion of the viral and endosomal membranes occurs (17,20,22). This results in the release of the nucleocapsid into the cytoplasm. Surprisingly, GP64 is closely related to the envelope fusion protein of the Thogoto virus genus of the Orthomyxoviridae, which are minus strand RNA viruses (24,25).Recently the sequences of the 161-kb Lymantria dispar MNPV (LdMNPV) (18), 136-kb Spodoptera exigua MNPV (15), and 178-kb Xestia c-Nigrum GV (XcGV) (11) genomes have been reported. A striking feature of these genomes is the lack of an identifiable homolog to gp64. The fact that the life cycle of LdMNPV is similar to those of AcMNPV and OpMNPV suggested that it must express a different envelope fusion protein. Computer-assisted analyses of the LdMNPV genome identified a single 676-amino-acid product of LdMNPV open reading frame (ORF) 130 (ld130), which was predicted to have both a ...

The Autographa californica multinucleocapsid nuclear polyhedrosis virus (AcMNPV), which is used for the overexpression of eukaryotic genes and is being engineered for possible use as a viral insecticide, has a circular, supercoiled genome of approximately 128 kilobases. Despite its widespread use, little is known about the mechanism by which AcMNPV replicates. Evidence is presented in this report that AcMNPV origins of DNA replication are repeated sequences each containing several closely related imperfect palindromes that are present in six regions distributed around the genome. Although AcMNPV infection-dependent plasmid replication was initiated by a single complete palindrome, the amount of replication was substantially increased in plasmids containing six or eight palindromes.

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