Force generating protein of eukaryotic cilia and flagella. Produces force towards the minus ends of microtubules. Dynein has ATPase activity; the force-producing power stroke is thought to occur on release of ADP. Required for assembly of the I1 inner arm complex and its targeting to the appropriate axoneme location. Also required for phototaxis. The I1 inner arm complex (also known as the f dynein complex) is a two-headed isoform composed of two heavy chains (1-alpha and 1-beta), three intermediate chains and three light chains. I1 occupies a specific position proximal to the first radial spoke and repeats every 96 nm along the length of the axoneme. By deflagellation. Dynein heavy chains probably consist of an N-terminal stem (which binds cargo and interacts with other dynein components), and the head or motor domain. The motor contains six tandemly-linked AAA domains in the head, which form a ring. A stalk-like structure (formed by two of the coiled coil domains) protrudes between AAA 4 and AAA 5 and terminates in a microtubule-binding site. A seventh domain may also contribute to this ring; it is not clear whether the N-terminus or the C-terminus forms this extra domain. There are four well-conserved and two non-conserved ATPase sites, one per AAA domain. Probably only one of these (within AAA 1) actually hydrolyzes ATP, the others may serve a regulatory function. A construct encoding the first 989 amino acids but lacking the motor domain is able to assemble I1 complexes and target them to their correct location on the axoneme, partially restores motility and fully rescue phototaxis. Cells swim slowly with aberrant waveforms, and are unable to phototax.