(a) Structures of TTP subunits from different Siphoviridae-like tails highlighting regions involved in quaternary interactions: N-terminus (blue), long-loop (yellow), extended helix/loop in T4 (orange), domain 2 in YSD1 (green), and C-terminus (red). Other α-helices and β-sheets are coloured in pale orange and lilac, respectively. The Ig-like domains of λ and T5 are highlighted in pink. (b) Hexameric rings of Siphoviridae-like TTP structures with a single subunit coloured in a rainbow representation from N- to C-terminus. Structures: T4 gp19 (PDB: 5W5F) [44]; RcGTA g9 (PDB: 6TEA) [52]; 80α gp53 (PDB: 6V8I) [48]; SPP1 gp17.1 (PDB: 6YEG) [50]; λ gpV (PDB: 6P3E) [51]; YSD1 YSD1_22 (PDB: 6XGR) [33]; and T5 pb6 (PDB: 5NGJ) [49]. Images were generated in UCSF Chimera version 1.14 [34].