GP5 and infection: We also found that: (1) gp5OB-fold interacts with the baseplate hub protein gp27 located at the tip of the tail tube and thus is required for incorporation of the protein into the T4 particle; (2) the substrate-binding cleft of gp5Lys is identical to that of T4L; (3) gp5β forms a needle that could pierce the outer membrane of the cell during infection; (4) the maturational cleavage is in the linker connecting gp5Lys with gp5β (gp5*, therefore, consists of gp5OB-fold and gp5Lys) (Figure 1).