FIG 1 .

A complementation assay demonstrated that the URR is required for long-term genome maintenance. (A) Diagram of deletions made in the background of the HPV18 genome. The ΔER replicon (deleted region highlighted in green) lacks part of the E7 and E1 open reading frames. The 3′ end (L1) of the entire URR and part of the E6 gene are deleted from ΔURR (blue). A large region of the L1 and L2 genes is deleted from ΔLR. (B) Different subgenomic replicons (or pUC18 as a control) were cotransfected with the HPV18 genome into primary HFKs. Low-molecular-weight DNA was extracted at different time points, digested with DpnI and a linearizing enzyme, and then analyzed by Southern blotting. Colored arrowheads indicate the positions of the HPV18 genome (black), ΔER (green), and ΔLR (red). A representative blot is shown. Each replicon was tested in similar assays at least three times.