Abstract
Actin from Tetrahymena pyriformis has been purified by monitoring the presence of the actin gene product with an antiserum against a synthetic N-terminal peptide deduced from the nucleotide sequence of the Tetrahymena actin gene that we cloned previously. This highly purified Tetrahymena actin shares many essential properties with ubiquitous actin, including ion-dependent polymerization to microfilaments, binding with muscle heavy meromyosin to form arrowheads, and activation of the Mg2+-ATPase of muscle myosin subfragment 1. On the other hand, some properties of this purified Tetrahymena actin clearly differ from those of muscle actin: (i) Tetrahymena actin has 8 times less ability to activate the Mg2+-ATPase of muscle myosin subfragment 1 than muscle actin; (ii) Tetrahymena actin did not bind to phalloidin at all; (iii) Tetrahymena actin did not inhibit DNase I activity at all. In general, Tetrahymena actin has very unusual properties when compared to other actins described so far. This actin is expected to provide important clues for elucidating problems concerning the relationships between the structural and functional domains in an actin molecule.