Fig. 3.

Schematic of selected assembly states for PR-A interactions at the MMTV promoter. MMTV promoter structure is as described in Fig. 1a. PR-A monomers (filled circle) can either dimerize in solution (k_di) or bind at a half-site (k₁). A solution dimer can bind at the palindromic site (k₂). Two monomers bound at half-sites cooperatively interact in a pairwise fashion (k_c1). Non-additive cooperativity induced by addition of a third monomer to the half-sites is accounted for by k_c2. Saturation of the MMTV promoter is linked to a third cooperative interaction between the palindrome and the three half-sites (k_c3).