ABSTRACT
This chapter explains that the primary force-generating event in a cilium is the ATP-driven cyclic movements of ciliary dynein—the first microtubule-based motor protein to be discovered. It suggests that the frequency with which cilia and flagella beat responds to environmental factors, especially in free-living organisms. The studies on cilia just described led to the eventual isolation and characterization of ciliary dynein, the first microtubule motor protein discovered. Ciliary dynein is a very large multisubunit protein with a head region containing a tubulin-activated ATPase activity and a tail portion that mediates ATP-insensitive binding to microtubules. Both a protein phosphatase and a cAMP-dependent protein kinase can be isolated from ciliary axonemes. In contrast to the loosely defined arrangement of microtubules in an axon or dendrite, those in cilia and in many other microtubule-containing structures of protozoa have a very precise and often complex pattern in cross-section.
