Identification of a kinesin‐like microtubule‐based motor protein in Dictyostelium discoideum.

Dictyostelium discoideum, a unicellular eukaryote amenable to both biochemical and genetic dissection, provides an attractive system for studying microtubule‐based transport. In this work, we have identified microtubule‐based motor activities in Dictyostelium cell extracts and have partially purified a protein that induces microtubule translocation along glass surfaces. This protein, which sediments at approximately 9S in sucrose density gradients and is composed of a 105 kd polypeptide, generates anterograde movement along microtubules that is insensitive to 5 mM NEM (N‐ethyl‐maleimide) but sensitive to 200 microM vanadate, and has similar nucleotide‐dependent microtubule binding properties to those of kinesins purified from mammals, sea urchin and Drosophila. This kinesin‐like molecule from Dictyostelium, however, is immunologically distinct from bovine and squid neuronal kinesins and supports microtubule movement on glass at four‐fold greater velocities (2.0 versus 0.5 microns/sec). Furthermore, AMP‐PNP (adenylyl imidodiphosphate), which promotes attachment of previously characterized kinesins to microtubules, decreases the affinity of the Dictyostelium kinesin homolog for microtubules. Thus, an AMP‐PNP‐induced rigor binding may not be a characteristic of kinesins from lower eukaryotes.