Stimulates the viral DNA replication. The virus utilizes both cellular and viral PCNAs during viral DNA replication in order to produce budded virus (BV). In addition, stimulates the expression of late genes 38K and VP39 by promoting the transcription of IE2. Transcribed early (from 2 through 6 hours post-infection) but not late (12 to 24 hours post-infection) in infection. Belongs to the PCNA family.