Breathing down the neck of Unc104

The Unc104/Kif1A class of kinesins transports synaptic vesicle precursors along microtubules with high speed and processivity that has been proposed to depend on reversible dimerization between two poorly motile monomers. In this issue, Al-Bassam et al. (2003) discover a structural basis for regulation of motility by reversible dimerization.