The mutant gene product of a Tetrahymena cell-division-arrest mutant cdaA is localized in the accessory structure of specialized basal body close to the division furrow.

A division arrest mutant, cdaA, of Tetrahymena thermophila is known to have a temperature sensitive-defect in the determination of the division plane, and its gene product had been shown to be a protein designated as p85 (Mr = 85,000; pI = 4.7). Here the localization of p85 was shown to be the accessary structure of specialized basal body close to the division furrow by immunoelectron microscopy using anti-p85 antiserum.