The gene family has expanded from the early days of the molecular and bioinformatics era. cerevisiae revealed a redundant function of these Kinesin-5 family members for spindle assembly ( Hoyt et al., 1992 Roof et al., 1992). Similarly, simultaneous loss of function in Cin8p and Kip1p in S. Cloning and sequencing of these mutants ( Hagan and Yanagida, 1990 Kashina et al., 1997) revealed that the gene product encoded a 130 kDa protein with high similarity to the conventional kinesin (KHC/Kinesin-1) involved in motility in squid and mammalian brains. These mutants had malfunctions in spindle pole body separation and nuclear division and were unable to undergo mitosis. In the search for strains that were defective in cellular division at a restrictive temperature, screens of fungal libraries and fission yeast uncovered BimC ( Enos and Morris, 1990) and Cut7 ( Hagan and Yanagida, 1990), respectively, in the early 1990s. Genetic analysis provided the initial insight into the key mitotic role of this motor family.

Of the >16 different kinesin isoforms ( Wickstead and Gull, 2006), Kinesin-5 (BimC/Eg5/N-2/Kif11) family members were the first identified to be essential in mitosis. This permits transport and movement along the cytoskeletal track.

Like dynein and myosin, these proteins hydrolyze ATP and convert chemical energy into mechanical energy. Kinesins are the smallest and most abundant nanomotor in cells and the only canonical motor protein that is ubiquitous in all eukaryotes. We review what is known about how this nanomotor works, its place inside the cytoskeleton of cells, and its small-molecule inhibitors that provide a toolbox for understanding motor function and for anticancer treatment in the clinic. These data have, in turn, informed the function of motile kinesins on the whole, as well as spearheaded integrative models of the mitotic apparatus in particular and regulation of the microtubule cytoskeleton in general. Based on a multi-faceted analysis of this motor from numerous laboratories over the years, we have learned a great deal about the function of this motor at the atomic level for catalysis and as an integrated element of the cytoskeleton. Comprised of a homotetramer complex, its function primarily is to slide anti-parallel microtubules apart from one another. Perhaps the simplest player in mitotic spindle assembly, Kinesin-5 (also known as Kif11, Eg5, or kinesin spindle protein, KSP) is a plus-end-directed motor localized to interpolar spindle microtubules and to the spindle poles. The mitotic kinesins, by virtue of their potential therapeutic role in cancerous cells, have been a major focus of research for the past 28 years since the discovery of the canonical Kinesin-1 heavy chain.

Kinesin motor proteins comprise an ATPase superfamily that goes hand in hand with microtubules in every eukaryote.

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