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Updated: Jul 19, 2026
Dissecting Host-virus Interaction in Lytic Replication of a Model Herpesvirus
Published on: October 7, 2011
Functional characterization of Kaposi's sarcoma-associated herpesvirus ORF45 by bacterial artificial chromosome-based
Fan Xiu Zhu1, Xiaojuan Li, Fuchun Zhou
1Department of Microbiology, School of Dental Medicine, University of Pennsylvania, 240 S. 40th Street, Philadelphia, PA 19104, USA.
Abstract:
Open reading frame 45 (ORF45) of Kaposi's sarcoma-associated herpesvirus (KSHV) encodes an immediate-early protein. This protein is also present in virions as a tegument protein. ORF45 protein interacts with interferon regulatory factor 7 (IRF-7) and inhibits virus-induced type I interferon production by blocking activation of IRF-7. To define further the function of ORF45 and the mechanism underlying its action, we constructed an ORF45-null recombinant virus genome (BAC-stop45) by using a bacterial artificial chromosome (BAC) system. Stable 293T cells carrying the BAC36 (wild type) and BAC-stop45 genomes were generated. When monolayers of 293T BAC36 and 293T BAC-stop45 cells were induced with 12-O-tetradecanoylphorbol-13-acetate and sodium butyrate, no significant difference was found between them in overall viral gene expression and lytic DNA replication, but induced 293T BAC-stop45 cells released 10-fold fewer virions to the medium than did 293T BAC36 cells. When ORF45-null virus was used to infect cells, lower infectivity was observed than for wild-type BAC36. These results suggest that KSHV ORF45 plays roles in both early and late stages of viral infection, probably in viral ingress and egress.
Insights
Kaposi's sarcoma-associated herpesvirus open reading frame 45 (ORF45) protein is crucial for viral release and infectivity. Deleting ORF45 significantly reduced virion production and cell entry, impacting KSHV infection stages.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Kaposi's sarcoma-associated herpesvirus (KSHV) open reading frame 45 (ORF45) is an immediate-early and tegument protein.
- ORF45 interacts with interferon regulatory factor 7 (IRF-7), inhibiting type I interferon production.
Purpose of the Study:
- To elucidate the function of KSHV ORF45.
- To investigate the mechanism of ORF45's action in viral infection.
Main Methods:
- Construction of an ORF45-null recombinant KSHV genome (BAC-stop45) using a bacterial artificial chromosome (BAC) system.
- Generation of stable 293T cells harboring wild-type (BAC36) and ORF45-null (BAC-stop45) KSHV genomes.
- Induction of viral gene expression and lytic DNA replication in cell cultures.
Main Results:
- No significant difference in overall viral gene expression or lytic DNA replication between wild-type and ORF45-null KSHV.
- Induced ORF45-null cells released 10-fold fewer virions compared to wild-type.
- ORF45-null virus exhibited lower infectivity in cell infection assays.
Conclusions:
- KSHV ORF45 plays critical roles in both early (ingress) and late (egress) stages of the viral life cycle.
- ORF45 is essential for efficient virion release and cell-to-cell spread of KSHV.
