The P2 bacteriophage J protein lies at the edge of the baseplate. This family also includes a number of bacterial homologues, which are thought to have been horizontally transferred.

1: Bacteriophage P2: genes involved in baseplate assembly. Haggard-Ljungquist E, Jacobsen E, Rishovd S, Six EW, Nilssen O, Sunshine MG, Lindqvist BH, Kim KJ, Barreiro V, Koonin EV, et al.; Virology 1995;213:109-121. PMID:7483254