ABSTRACT
The history of research on dynein began with electron microscope images showing dynein ‘arms’ forming crossbridges between the doublet microtubules in a ciliary axoneme. The tail of cytoplasmic dynein binds to dynactin and adaptor proteins. Forming a ternary complex with dynactin and an adaptor protein rearranges the dynein heads in a parallel way; dynein molecules in this form can move processively for a long distance. The major clades of AAA+ domains include subunits that change the conformations of other proteins and others that induce changes in DNA. There is no sign of a close relative of cytoplasmic dynein in current prokaryotic cells, despite its likely existence before that of axonemal dynein. Based on the simpler structure of cytoplasmic dynein and sequence comparisons, I. R. Gibbons first proposed that the variety of axonemal dyneins evolved by gene duplication from cytoplasmic dynein.
