FIG. 4.

The E1 DBD binds as two monomers to the minimal ori. To determine if the E1 DBD binds as two monomers on the E1 palindrome, three quantities of E1(142–308), 0.4, 0.2, and 0.1 ng, were incubated together with 0.5 ng of E1(142–374), 18 pg of the E2 DBD, and probe containing the BPV minimal ori with a high-affinity E2 binding site in 10-μl binding reactions (lanes 10 to 12). The asterisk marks the mobility of an intermediate complex formed when E1(142–374) and E1(142–308) were mixed in the presence of the E2 DBD (lanes 3 and 7 to 9, respectively). The levels of binding by E1(142–308) in the absence of the E2 DBD and E1(142–374) are shown in lanes 4 to 6. Lanes 1 and 2 are markers for the binding of E1(142–374) and E1(142–308), respectively.