In the early 1980s, the molecular mechanisms for directed transport of organelles remained elusive. Of particular interest was the process of fast axonal transport, in which organelles are actively and rapidly transported in both anterograde and retrograde directions in neuronal axons. In 1985, an amazing series of articles culminated in the identification of kinesin as the molecular motor responsible for the fast axonal transport of organelles along microtubules.
Ron Vale and colleagues adopted an assay for the real-time observation of fast axonal transport in vitro that was developed by Robert Allen and Scott Brady (see Milestone 13), and showed that organelle transport occurred in an ATP-dependent manner and at a uniform rate along the isolated filaments. By combining video and electron microscopy, they succeeded in identifying these filaments as single microtubules. Vale and colleagues also observed that, like organelles, small plastic beads coated with axonal cytosol could move along microtubules and that glass coverslips coated with the same cytosol supported microtubule gliding across the surface — both of which are assays for motor activity that remain in common use today. Raymond Lasek and Brady then demonstrated that the non-hydrolysable ATP analogue 
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-imidoadenosine 5'-triphosphate (AMP-PNP) led to the stabilization of microtubule–organelle complexes, indicating that the ATPase responsible for fast axonal transport could be locked onto microtubules, thereby providing a useful tool for purification.
Using squid axons, Vale and colleagues isolated the motor protein by using AMP-PNP to stabilize the motor–microtubule interaction as a first-affinity purification step, followed by column chromatography. During the purification, they assayed the fractions for motor activity using microscopy-based in vitro assays. The purified protein that powered motility in vitro contained polypeptides of 110–120 kDa and 60–70 kDa, which were much smaller than the main polypeptide of dynein — the only other microtubule-dependent motor known at the time. Hence, a new motor was discovered and termed kinesin (from the Greek kinein, meaning to move).
"... laid the ground work for people to start thinking in terms of 'many motors'."
William Bement
While Vale and colleagues isolated kinesin from squid nervous tissue, Brady independently discovered a microtubule ATPase with the same molecular weight and properties as kinesin in the chicken brain. In the subsequent years, the development of screening and sequencing tools led the way towards genome-wide identification of motors related to kinesin, and this superfamily has grown to include microtubule plus-end-directed and minus-end-directed motors as well as motors that can crosslink, slide and depolymerize microtubules. These motors are intimately involved in a range of cellular phenomena other than axonal transport including, for example, intracellular transport and organization, mitosis and regulation of signalling pathways (see Further reading).
