Fig. 4.

Key molecular interactions of an auxin transcriptional complex. (A) ARFs (blue) dimerize in both the N-terminal dimerization domain (DD) and the PB1 domain for robust transcriptional activation. Secondary interactions in the PB1 domain stabilize an ARF dimer on the DNA. DB, DNA binding; DD, dimerization domain; MR, middle region; PB1, C-terminal interaction domain. (B) Spacing and orientation of ARF-binding sites may drive conformation of the flexible middle region (MR) upon DNA binding. PB1 interactions likely lock this conformation into place to create binding pockets for specific coactivators. (C) A monomeric IAA (green) can repress ARF activity. The decrease in ARF affinity when a single PB1 face is mutated suggests that an IAA optimally interacts with ARF dimers through both PB1 interfaces. It is possible that the IAA PB1 domain is sandwiched between the PB1 domains of an ARF dimer, creating a scaffold for the recruitment of repression machinery.