HTC1 TP901-1, being absent in mutants Portal TP901-1 ::Ter, Sfp TP901-1 ::Ter and MHP TP901-1 ::Ter, appears to be a functional analogue of SPP1 gp15, and can fit into the electron density map of the TP901-1 head-tail connector region during the pseudoatomic model construction of this phage [14, 42 ].
Source: wiktionary