Molecular comparison of promoter region of Varicella Zoster Virus (VZV) Oka and Dumas strains replication genes, 16 and 52

Current investigations indicate different in vitro infection patterns for Oka and Dumas strains. Infection of cells in culture with Dumas strain produces lower number of infectious particles while the Oka strain is highly infectious in vitro. It is postulated that weak expression of the replication genes in Dumas strain may be the reason for the attenuated phenotype.
The objective of this study was to analyze the sequences of the promoter region in two of the VZV replication genes, 16 and 52 by studying the level of expression of a reporter gene.
For this purpose, primers were designed from VZV published sequences to amplify the promoter regions of both genes using Polymerase Chain Reaction (PCR) technique. The amplicons were cloned in a lacZ reporter vector. Cotransfaction of 52-Oka reporter plasmid with virus major trans-activator (IE62) in Huh7 cells showed that the presence of 52-Oka promoter was up regulated by the IE 62 trans-activator in a dose dependent manner resulting in ß-gal levels approximately 4-fold higher than those observed with 52-Dumas promoter and 10-fold higher than basal levels. In addition cotransfection of 16-Oka reporter plasmid did not show any significant change in activity in comparison with 16-Domus-reporter plasmid.
Sequence determination of the promoter region in gene 52 indicated differences in 3 nucleotides in Dumas strain compared to Oka strain while no change was observed in the promoter sequences of gene 16 of the two strains.
It is hence postulated a relationship between mutations in the Dumas promoter of replication genes, and the lower infectivity of the Dumas strain.