FIG. 2.

Southern analysis of keratinocytes stably transfected with wild-type HPV31, E4M4 mutant, or E4M9 mutant genomes. Equal amounts of total DNA were isolated from keratinocytes harboring wild-type, E4M4, and E4M9 genomes at various passages and were examined by Southern analysis using a linearized HPV31 DNA genome as a probe. Two representative Southern blots from two different HFK cell lines are shown. (A) Wild type- and E4M9-transfected keratinocytes were able to stably replicate HPV genomes as episomes at various passages. (B) In contrast, E4M4-transfected keratinocytes were unable to be stably maintained as episomes at late passages. Three different migrating forms of HPV are indicated (integrated/multimeric, nicked circular, and supercoiled/episomal).