Structural component of the bacteriophage tail which consists of a contractile sheath, a tube and a baseplate. The central cylindrical segment of the tail consists of a rigid tube, composed of multiple copies of the tail tube protein. 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. Belongs to the T4-like viruses Gp19 protein family.