We have determined the full sequence of K2, a kinesin-related protein (KRP) in Dictyostelium discoideum. Sequence homology and domain organization placed K2 in the ncd/Kar3 subfamily of the C-terminal-type KRPs. Bacterially expressed, truncated K2 showed ATP-dependent binding to microtubules and microtubule-stimulated ATPase activity. K2-null cells grew and developed normally, suggesting overlapping functions of K2 with other microtubule motor(s). Overexpression of K2 caused partial mitotic arrest. Green fluorescent protein-tagged full-length K2 localized in the nucleus at the interphase and on the mitotic spindle during mitosis. These results suggest that K2 is a microtubule-dependent motor which may play some roles in mitotic spindles.
