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Herpes simplex ICP27 mutant viruses exhibit reduced expression of specific DNA replication genes
1Harvard Medical School, Boston, Massachusetts 02115, USA.
Abstract:
Herpes simplex virus type 1 mutants with certain lesions in the ICP27 gene show a 5- to 10-fold reduction in viral DNA synthesis. To determine how ICP27 promotes amplification of viral DNA, we examined the synthesis, accumulation, and stability of the essential viral replication proteins and steady-state levels of the replication gene transcripts throughout the course of ICP27 mutant virus infections. These studies reveal that in the absence of ICP27, expression of the UL5, UL8, UL52, UL9, UL42, and UL30 genes is significantly reduced at the level of mRNA accumulation. In contrast to that of these beta genes, ICP8 expression is unaltered in mutant virus-infected cells, indicating that ICP27 selectively stimulates only a subset of herpes simplex virus beta genes. Analysis of multiple ICP27 mutant viruses indicates a quantitative correlation between the ability of these mutants to replicate viral DNA and the level of replication proteins produced by each mutant. Therefore, we conclude that the primary defect responsible for restricted viral DNA synthesis in cells infected with ICP27 mutants is insufficient expression of most of the essential replication genes. Of further interest, this analysis also provides new information about the structure of the UL52 gene transcripts.
Insights
Herpes simplex virus type 1 (HSV-1) ICP27 protein is crucial for viral DNA replication. Mutants lacking functional ICP27 show reduced DNA synthesis due to insufficient expression of essential viral replication genes.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Herpes simplex virus type 1 (HSV-1) DNA replication is essential for its life cycle.
- The infected cell protein 27 (ICP27) is a key regulatory protein in HSV-1 infection.
- Previous studies indicated ICP27's role in viral DNA synthesis, but the precise mechanism was unclear.
Purpose of the Study:
- To elucidate the mechanism by which ICP27 promotes viral DNA amplification.
- To investigate the impact of ICP27 on the expression of essential viral replication proteins and their corresponding gene transcripts.
- To determine if ICP27 selectively regulates a subset of viral genes.
Main Methods:
- Analysis of viral DNA synthesis in HSV-1 ICP27 mutant infections.
- Examination of the synthesis, accumulation, and stability of viral replication proteins.
- Quantification of steady-state mRNA levels for replication genes in mutant-infected cells.
- Comparison of multiple ICP27 mutant viruses with varying replication efficiencies.
Main Results:
- HSV-1 ICP27 mutants exhibited a 5- to 10-fold reduction in viral DNA synthesis.
- Absence of ICP27 led to significantly reduced mRNA accumulation for several key replication genes (UL5, UL8, UL52, UL9, UL42, UL30).
- ICP8 expression remained unaltered in ICP27 mutant infections, indicating selective regulation.
- A quantitative correlation was observed between viral DNA replication capability and replication protein levels in different ICP27 mutants.
- Novel information regarding the structure of UL52 gene transcripts was obtained.
Conclusions:
- The primary defect in ICP27 mutant viruses leading to restricted viral DNA synthesis is the insufficient expression of essential viral replication genes.
- ICP27 selectively stimulates the expression of a subset of HSV-1 beta genes involved in DNA replication.
- ICP27 plays a critical role in coordinating the expression of genes required for efficient viral DNA amplification.