Structure and organization of radial spokes in cilia of Tetrahymena pyriformis

The structure and organization of radial spokes, the principal components between each of the peripheral doublet microtubules and the central sheath which surrounds the central pair of microtubules have been described in Tetrahymena pyriformis cilia. The radial spokes are grouped in triplets and are attached to the A-microtubule of each peripheral doublet at intervals of 200/280/360 A, the 200 A spacing being most distal to the base of the cilium. The radial spoke triplets are organized in the axoneme in a double helix with a pitch of 4,680 A. A method for determining the helical disposition by correcting for doublet sliding is presented.