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An apoptosis-inhibiting gene from a nuclear polyhedrosis virus encoding a polypeptide with Cys/His sequence motifs
M J Birnbaum1, R J Clem, L K Miller
1Department of Genetics, University of Georgia, Athens 30602.
Abstract:
Two different baculovirus genes are known to be able to block apoptosis triggered upon infection of Spodoptera frugiperda cells with p35 mutants of the insect baculovirus Autographa californica nuclear polyhedrosis virus (AcMNPV):p35 (P35-encoding gene) of AcMNPV (R. J. Clem, M. Fechheimer, and L. K. Miller, Science 254:1388-1390, 1991) and iap (inhibitor of apoptosis gene) of Cydia pomonella granulosis virus (CpGV) (N. E. Crook, R. J. Clem, and L. K. Miller, J. Virol. 67:2168-2174, 1993). Using a genetic complementation assay to identify additional genes which inhibit apoptosis during infection with a p35 mutant, we have isolated a gene from Orgyia pseudotsugata NPV (OpMNPV) that was able to functionally substitute for AcMNPV p35. The nucleotide sequence of this gene, Op-iap, predicted a 30-kDa polypeptide product with approximately 58% amino acid sequence identity to the product of CpGV iap, Cp-IAP. Like Cp-IAP, the predicted product of Op-iap has a carboxy-terminal C3HC4 zinc finger-like motif. In addition, a pair of additional cysteine/histidine motifs were found in the N-terminal regions of both polypeptide sequences. Recombinant p35 mutant viruses carrying either Op-iap or Cp-iap appeared to have a normal phenotype in S. frugiperda cells. Thus, Cp-IAP and Op-IAP appear to be functionally analogous to P35 but are likely to block apoptosis by a different mechanism which may involve direct interaction with DNA.
Insights
Researchers identified a new baculovirus gene, Op-iap, from Orgyia pseudotsugata NPV that inhibits apoptosis. This gene functionally replaces the p35 gene in Autographa californica NPV, suggesting a novel mechanism for blocking programmed cell death in insect cells.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Baculovirus infection can trigger apoptosis in insect cells.
- Two known baculovirus genes, Autographa californica nuclear polyhedrosis virus p35 and Cydia pomonella granulosis virus inhibitor of apoptosis gene (Cp-iap), can block this apoptosis.
- Identifying additional apoptosis-inhibiting genes is crucial for understanding baculovirus-host interactions.
Purpose of the Study:
- To identify novel baculovirus genes that inhibit apoptosis.
- To characterize a newly isolated gene, Op-iap, from Orgyia pseudotsugata NPV for its ability to substitute for the p35 gene.
- To elucidate the functional and structural properties of Op-iap and its encoded protein.
Main Methods:
- Genetic complementation assay using p35 mutant baculoviruses.
- Nucleotide sequencing of the isolated Op-iap gene.
- Bioinformatic analysis of the predicted Op-iap polypeptide sequence.
- Phenotypic analysis of recombinant viruses in Spodoptera frugiperda cells.
Main Results:
- A gene, Op-iap, was isolated from Orgyia pseudotsugata NPV that functionally complements p35 mutants.
- Op-iap encodes a 30-kDa protein with 58% amino acid identity to Cp-IAP.
- Both Op-IAP and Cp-IAP possess a C3HC4 zinc finger-like motif and N-terminal cysteine/histidine motifs.
- Recombinant viruses expressing Op-iap or Cp-iap showed a normal phenotype in Spodoptera frugiperda cells.
Conclusions:
- Op-iap is a functional homolog of the baculovirus p35 gene.
- Op-iap and Cp-iap (inhibitors of apoptosis) are functionally analogous to P35 but likely employ a distinct mechanism to inhibit apoptosis, potentially involving DNA interaction.
- These findings expand the repertoire of known baculovirus anti-apoptotic genes and suggest diverse strategies for viral evasion of host cell death pathways.