Background: Open reading frame 58 (ORF58) of varicella-zoster virus (VZV) lies at the 3'end of the Unique long (UL) region and its functional is unknown. In order to clarify whether ORF58 is essential for the growth of VZV, we constructed a deletion mutant of ORF58 (pOka-BACDelta58) from the Oka parental genome cloned into a bacterial artificial chromosome (pOka-BAC).
Results: The ORF58-deleted virus (rpOkaDelta58) was reconstituted from the pOka-BACDelta58 genome in MRC-5 cells, indicating that the ORF58 gene is non-essential for virus growth. Comparison of the growth rate of rpOkaDelta58 and recombinant wild-type virus by assessing plaque sizes revealed no significant differences between them both in MRC-5 cells and malignant melanoma cells.
Conclusion: This study shows that the ORF58 gene is dispensable for viral replication and does not affect the virus' ability to form plaques in vitro.