Baseplate protein that forms, together with gp48, the baseplate-tail tube junction. The tail tube first 2 annuli are formed by gp48 and gp54, which are in continuation of the spike complex. Involved in the tail assembly. Morphogenesis of the baseplate is completed by association of gp48 and gp54, which bind the upper part of the baseplate dome to form the platform for polymerization of the tail tube. Homohexamer (PubMed:27193680). The tube second annulus is composed of a gp54 hexameric ring. Interacts with the tail tube protein gp19. Interacts with the first layer of sheath proteins gp18. Part of the baseplate macromolecular complex which consists of gp5, gp5.4, gp27 (central spike complex); gp6, gp25, gp53 (inner baseplate); gp7, gp8 (intermediate baseplate); gp9, gp10, gp11, gp12 (peripheral); gp48 and gp54 (proximal region of the tail tube). Present in 6 copies in the baseplate. Expressed in the late phase of the viral replicative cycle.