Dynein was first identified and named by Ian Gibbons in the 1960s as an ATPase that could be extracted from cilia and flagella. The number of papers written per year has increased steadily ever since (Fig. 1.1). The complex structural and functional secrets of this microtubule (MT) motor were very gradually unlocked. In Table 1.1 we summarize some of the important advances that were made in the past half-decade. Recently, however, progress has accelerated greatly, thanks to a variety of tools that were not available originally, such as sequencing of whole genomes, success in producing recombinant dynein, EM cryo-microscopy and tomography, and singleparticle measurements. This makes it difficult to summarize all important new contributions. Current understanding of dynein’s structure and motile mechanism, and its wide range of roles in vivo, are described in more detail in subsequent chapters. Handbook of Dynein Edited by Keiko Hirose and Linda A. Amos Copyright © 2012 Pan Stanford Publishing Pte. Ltd. www.panstanford.com

Dynein was first seen in an electron microscope (EM) as two rows of “arms” on each doublet MT in thin sections of flagella (see Chapters 10 to 12) whose fine structure had been preserved with a new chemical fixative, glutaraldehyde [1]. The image in Fig. 1.2 i is an example of similar results obtained by Gibbons and Grimstone [23], who improved the contrast in their sections by introducing a novel staining method. A few years later, a protein having ATPase activity was extracted from Tetrahymena cilia and named “dynein” by Gibbons and Rowe [24]. A fraction that was characterized by ultracentrifugation as 14S molecules was seen by EM (Fig. 1.2 ii) as individual globular particles; another fraction, consisting of larger complexes appeared to be a longish linear polymer (30S dynein), whose identity is still a little mysterious. A decade later, outer arm of Tetrahymena cilia, before and after extraction from axonemes, appeared in negative stain as a linear complex of three subunits ([130], Fig. 1.2 iii). It became also clear that outer arms are arranged with a periodicity of ~24 nm in axonemes. Conformational changes were observed between the dynein arms crossbridging two-doublet MTs and those unbound to the B-tubule ([131], Fig. 1.2 iv), and between the arms in the presence and absence of ATP [120]. It was found that the binding of arms to the B-tubule is nucleotide-dependent, but there was controversy as to whether the arms dissociate from the Btubule with ATP. In 1982, Goodenough & Heuser [32] first saw a thin stalk extending from the globular dynein head, in axonemes that had been rapidly frozen to preserve their structure (Fig. 1.2 v-viii). Conformational changes in the presence/absence of ATP were also clearly demonstrated (Fig. 1.2 v,vii). At this point, therefore, the main structural features of dynein molecules (Chapters 4, 5, 6, and 11) had already been observed but they could not

properly be understood until the HC sequence had been determined in 1991 [28, 85], which paved the way both for identification of the MT-binding region in 1997 [22, 61] and recognition of dynein as a member of the superfamily of AAA+ proteins in 1999 [82].