High-frequency phenotypic reversion and pathogenicity of an acyclovir-resistant herpes simplex virus mutant

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Acyclovir resistance in herpes simplex virus (HSV) can arise from mutations in the viral thymidine kinase (TK) gene.
• A specific double-guanine insertion mutation in the TK gene was identified in a resistant clinical isolate.

Purpose of the Study:

• To investigate the genetic instability and phenotypic consequences of a double-guanine insertion mutation in the HSV TK gene.
• To determine the impact of this mutation on viral TK activity and pathogenicity.

Main Methods:

• Engineering the double-guanine insertion mutation into the HSV-1 KOS strain.
• Generating virus stocks from single plaques and analyzing TK activity via plaque autoradiography.
• Assessing viral reactivation from latency in mouse ganglia and TK activity in reactivated virus.

Main Results:

• Engineered virus stocks showed a high frequency of phenotypic reversion, with ~3% of plaques exhibiting high TK activity.
• The virus demonstrated reactivation from latency in mouse ganglia.
• A fraction of reactivated virus carried the additional G insertion, displaying high TK activity.

Conclusions:

• The double-guanine insertion mutation in the HSV TK gene leads to significant genetic instability and high rates of phenotypic reversion.
• This genetic instability, characterized by increased TK activity, may contribute to the pathogenicity of HSV during reactivation from latency.