Varicella-zoster virus open reading frame 4 protein is functionally distinct from and does not complement its herpes simplex virus type 1 homolog, ICP27

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Varicella-zoster virus (VZV) open reading frame 4 (ORF4) encodes a protein homologous to herpes simplex virus type 1 (HSV-1) ICP27.
• Gene location and amino acid sequence similarity suggest functional parallels between VZV ORF4 and HSV-1 ICP27.

Purpose of the Study:

• To investigate the functional similarities and differences between VZV ORF4 and HSV-1 ICP27.
• To characterize the transactivation and transrepression activities of VZV ORF4.
• To elucidate the roles of these proteins in viral replication.

Main Methods:

• Transient expression assays were performed to compare ORF4 and ICP27 activities.
• Vero cell lines expressing VZV ORF4 under an inducible metallothionein promoter were constructed.
• The ability of VZV ORF4 to upregulate VZV target plasmids and complement HSV-1 ICP27 mutants was assessed.

Main Results:

• VZV ORF4 directly transactivates promoters, unlike HSV-1 ICP27 which requires co-transactivators.
• VZV ORF4 exhibits no apparent transrepressing activity, whereas ICP27 can transrepress.
• VZV ORF4 upregulated VZV target plasmids but did not efficiently complement HSV-1 ICP27 mutants.

Conclusions:

• Despite structural homology, VZV ORF4 and HSV-1 ICP27 display different functional properties in transient expression assays.
• These distinct behaviors suggest that VZV ORF4 and HSV-1 ICP27 may fulfill different roles during their respective virus replication cycles.