By eliminating motors that work in either antagonistic or redundant pairs, Cottingham et al. find that Saccharomyces cerevisiae can function with just two microtubule-based motors (page 335). Budding yeast does not require microtubules for protein trafficking, so the two motors define a minimal set for constructing and then using a mitotic spindle.
Cottingham et al. start by rounding out the roles for motors in nuclear positioning. The kinesins Kar3p and Kip3p work with a dynein (Dyn1p) to oppose another kinesin (Kip2p). The removal of Kip2p compensates for the loss of dynein plus either Kar3p or Kip3p; the remaining motor opposes a non-microtubule force (possibly actin-based streaming) that disrupts nuclear positioning.
But Kar3p and Kip3p also have an essential role in the nucleus, where they work together to promote spindle assembly. For Kar3p, at least, this function opposes the BimC...
