a Structure of the PDE3ACAT-SLFN12-DNMDP heterotetramer. PDE3ACAT (dark and light blue) and SLFN12 (green and magenta) are shown in a surface and cartoon representation, respectively. The loop regions between 779–799 and 1029–1068, which do not show density in the Cryo-EM maps, are indicated by dashed lines on one PDE3A monomer (light blue). The zinc ions of SLFN12 are shown as gray spheres. b Detailed view of the SLFN12 monomer structure. A schematic showing the different regions of SLFN12 is shown at the top with the structure of the dimer shown below. One monomer is shown in a surface representation (white) and the other in cartoon representation with different regions color-coded to match the schematic. Residues that are involved in stabilizing contacts within the C-terminal domain and between the N- and C-terminal domains (F548, A12, and P519) are indicated. BD bridging domain. c Summary of the SLFN12 dimer interface interactions. Each of the points of contact is denoted by a key residue, which is shown in the top left corner of each panel. The backbone of each monomer, and the labels of the residues shown, are colored green or magenta depending on which monomer they come from. The labels for the monomer in magenta also have a prime mark to indicate that they are from the other monomer.