Fig. 4:

Rev7 dimer is the organizing center of Polζ holoenzyme. a, Rev7 dimer presents a novel head-to-tail arrangement (left) in comparison to other HORMA family members (right, PDB ID: 2V64). The C-terminal seatbelt region is highlighted in cyan. Both Rev7 subunits are in the closed state with Rev7_A binding RBM1 and Rev7_B binding RBM2. b, Both Rev7 subunits are required for assembly of the Polζ holoenzyme. Structure and cryo-EM density details of the Rev7 dimer interface with Rev3, Pol31 and Pol32_N. RBM1 and RBM2 share a consecutive proline-proline motif that interacts with similar set of residues (Y27, F141, L54, Y57, for example) from both monomers. Interactions at the Rev7_A and RIR interface that further stabilize the Rev7_A:Rev7_B dimer are shown. In addition, interactions of Rev7_B with Pol31_PDE–Pol32_N depicted here aid in restricting the movement of Pol31–Pol32_N subcomplex relative to Rev3.