FIG. 8.

Comparison of the arrangements of T-antigen binding sites in the SV40 ori with that of the proposed E1 binding sites in the BPV minimal ori. (A) The BPV minimal ori may contain four E1 binding sites. Binding sites 2 and 4, arranged in a head-to-head orientation, are used for the binding of two E1 monomers in the E1E2-ori complex. Binding sites 2 and 4, which are also oriented head to head, overlap binding sites 1 and 3 by three nucleotides. (B) The SV40 ori consists of four T-antigen binding sites of which T antigen binds primarily to sites 1 and 3, which are also oriented head to head.