Roles of two homotetrameric kinesins in sea urchin embryonic cell division

To improve our understanding of the roles of microtubule cross-linking moto rs in mitosis, we analyzed two sea urchin embryonic kinesin-related protein s. It is striking to note that both of these proteins behave as homotetrame rs, but one behaves as a more compact molecule than the other. These observ ations suggest that these two presumptive motors could cross-link microtubu les into bundles with different spacing. Both motors localize to mitotic sp indles, and antibody microinjection experiments suggest that they have mito tic functions. Thus, one of these kinesin-related proteins may crosslink sp indle microtubules into loose bundles that are "tightened" by the other.