C. elegans contains a microtubule binding protein that resembles both dynein and kinesin. This protein has a MgATPase activity and copurifies on both sucrose gradients and DEAE Sephadex columns with a polypeptide of Mr approximately 400 kd. The ATPase activity is 50% inhibited by 10 μM vanadate, 1 mM N-ethyl maleimide, or 5 mM AMP-PNP; it is enhanced 50% by 0.2% Triton. The 400 kd polypeptide is cleaved at a single site by ultraviolet light in the presence of ATP and vanadate. In these ways, the protein resembles dynein. The protein also promotes ATP-dependent translocation of microtubules or axonemes, "plus" ends trailing. This property is kinesin-like; however, the motility is blocked by 5 μM vanadate, 1 mM N-ethyl maleimide, 0.5 mM ATP-γ-S, or by ATP-vanadate-UV cleavage of the 400 kd polypeptide, characteristics that differ from kinesin. We propose that this protein is a novel microtubule translocator.
Bibliographical noteFunding Information:
Taxol was a generous gift from Dr. Matthew Suffness, Natural Products Division, National Cancer Institute. This work was supported by grants ACS BC-498 and NIH 37773. J. Ft. M. gratefully acknowledges the hospitality of John Kilmartin and the C. elegans research group at the MRC Laboratory of Molecular Biology, Cambridge, UK, where a study of nematode microtubule proteins was begun with support from an Eleanor Roosevelt International Cancer Scholar award from the UICC. We would like to thank Derek Stemple, George HartzelI, Dr. Guy Vigers, and Dr. Stanley Cohn (National Jewish Center for Immunology and Respiratory Medicine) for their help and computer expertise. We would also like to thank Dr. Robley Williams, Jr. for the gift of phospho-cellulose-purified tubulin.