Forms the central cylindrical rigid tube, which is surrounded by the outer contractile sheath assembled from gp18 subunits. The tail tube first 2 annuli are formed by gp48 and gp54, which are in continuation of the spike complex. During infection, contraction of the sheath drives the central tube through the host outer membrane, creating a channel for DNA ejection from the capsid into the host cell. Homohexamer. The tube is composed of gp19 hexameric rings. Interacts with gp54. Belongs to the T4-like viruses Gp19 protein family.