Figure 6.

Cryo-EM structural details. (A, left) PP7-PP7 dimer threefold organization, (A, right) expanded view of one single-chain dimer, with AYGG linker (green), N-terminal Ser (cyan), and C-terminal Arg (purple) residues shown in stick representation. (B) Comparison of particles bearing the a-loop insertion and C-terminal ZZ-domain extension. Arrows mark regions of poorly resolved amino acid density in the reconstruction of the PP7-a-loop-PP7 particle following the initial Ala residue of the a-loop (left) and following the last Arg residue at the C-terminus (Arg127) (right). Circles delineate well-resolved linker loop density for the PP7-PP7-ZZ particle (left) and the Gly residue that starts the linkage to the ZZ-domain but not the rest of that domain (right).