FIG. 6.

Model of cooperative binding of E1 and E2 to the BPV minimal ori. (A) Cooperative binding between E1 and E2 involves two separate interactions: interaction 1 between the E1 and E2 DBDs and interaction 2 between the E1 helicase domain and the E2 activation domain (AD). As the first required step in the cooperative binding of E1 and E2 on the BPV minimal ori, the E2 DBD interacts with the E1 DBD (interaction 1). This interaction results in bending or kinking of the DNA. As a consequence of the induced DNA bend, the E2 activation domain is placed in a position where it can effectively interact with the E1 helicase domain. The productive interaction between the E2 activation domain and E1 completes the second step in the cooperative binding of E1 and E2 on the ori. (B) Mutations in the E2 DBD which result in failure to interact with the E1 DBD result in loss of the interaction between E1 and E2 despite a wt and functional E2 activation domain.