Figure 14. Structure of the bacteriophage T4 tail in the extended (A) and contracted (B) conformations. Constituent proteins are shown in different colors. The contractile tail sheath is shown in green. (C) Structure of the tail sheath protein mutant, gp18M, containing 3 out of 4 domains of gp18. Domain I is in blue, domain II is in olive green, domain III is in orange red. Residues 454–470 and the last 27 C-terminal residues of gp18M are shown in cyan. (A) was reproduced from reference 137, (B) from reference 147, and (C) from reference 146.