A 65-year-old woman with multiple myeloma on chemotherapy develops a painful vesicular rash along her right thoracic dermatome. She is diagnosed with herpes zoster and started on oral famciclovir. Famciclovir is a prodrug that is rapidly deacetylated and oxidized to penciclovir, which then undergoes phosphorylation. Which of the following best describes the antiviral mechanism of famciclovir (penciclovir)?