The head-tail connector of bacteriophage 29 is composed of 12 36 kDa subunits with 12 fold symmetry. It is the central component of a rotary motor that packages the genomic dsDNA into pre-formed proheads. This motor consists of the head-tail connector, surrounded by a 29-encoded, 174-base, RNA and a viral ATPase protein.
Jiyao W et al.(2023). "The conserved domain database in 2023.",