FIG 2.

Fonticin contractile particles in their native, contracted, and decomposed forms, with sheath and tube visualized by TEM. The native fonticin particle is 124 nm long (W) and 18 nm wide (X). After attachment of tail fibers to the specific receptor, the sheath is contracted, which enables the tube to perforate cytoplasmic membrane. The contracted sheath is 54 nm long (Y) and 24 nm wide (Z). After contraction, the sheath is usually released from the tube.