Kinesin heavy chain and kinesin-related polypeptides (KRPs) comprise a family of motor proteins with diverse intracellular transport functions. Using pan-kinesin peptide antibodies that react with these proteins, we have previously purified from sea urchin eggs a trimeric microtubule-binding and bundling protein, KRP (85/95) (ref. 8) comprising subunits of M(r) 115,000 (115K), 95K and 85K. We report here that kinesin-related genes encode the 85K and 95K subunits, and that the protein can be immunoprecipitated from cytosol as a trimeric complex using an 85K monoclonal antibody. We also find that purified KRP(85/95) directs movements towards the 'plus' ends of microtubules. To our knowledge, this protein is the first kinesin-related motor to be purified from its natural host cell in a native multimeric state.