B204 structure. (A) Ribbon diagram of a B204 monomer bound to AMPPCP and Mg2+ (green sphere) (PBD: 4KFU) . The regions highlighted in red indicate the conserved P9-motif described for the PRD1-like lineage of viruses . (B) A hexamer model of B204 shown in rainbow hues (blue to red) generated by aligning six monomers of chain A of the AMPPCP B204 structure (PDB: 4KFU) onto each of the FtsK monomers in the FtsK hexamer (PDB: 2IUU) using the program UCSF Chimera . According to our hypothesis the C-terminal part of B204 (orange to red) lies on the capsid distal side. A short stretch of dsDNA (black and blue helix) is modelled into the channel formed by the monomers. (C) A radially depth-cued isosurface representation (at 2 σ above the mean) of the 20-Å resolution reconstruction of STIV2 (EMDB: 1679)  with one of the turrets replaced by our hexameric model of B204 (surface representation in rainbow hues as in panel B). The figure was rendered in UCSF Chimera .