Plays a role in morphogenesis of the virion head after genome packaging. Presumably interacts with the portal vertex to stabilize the packaged DNA within the head after packaging. Probably binds to the head-tail connector protein gp8. Monomer in solution, assembles into hexamers on the prohead. May bind gp8 and portal protein (Potential). Probably part of the head-tail connector. Belongs to the lambda phage gpW family.