Structural conformation of the ciliary ATPase dynein.

The ATPase dynein forms part of a mechanoohemically active complex responsible for the sliding filament mechanism of ciliary and flagellar motion. Extraction of demembranated cilia from the lamellibranch mollusc Unio or the protozoan Tetrahymena by 0.5 m-KCl solubilizes the outer rows of dynein and, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, releases the A form (Mr 360,000) of dynein into solution. Negative contrast electron microscopy of the solubilized dynein fraction reveals an homogeneous array of 93 Å particles that we identify as the ATPase dynein in its monomeric form. Because of the method of dynein extraction, the conformation of the molecule, and the size and shape of the outer arms in situ, we suggest that monomeric dynein is only one part of a larger, non-covalently joined molecular complex that forms the entire arm. When KCl-extracted axonemes are viewed by negative contrast but prior to fractionation of the dynein, individual arms can be seen that comprise three to four of the 93 Å subunits, thus suggesting that each arm is a multisubunit polymer of dynein or dynein-like molecules.