Identification and characterization of a novel microtubule-based motor associated with membranous organelles in tobacco pollen tubes

Pollen tube growth depends on the differential distribution of organelles a nd vesicles along the tube. The role of microtubules in organelle movement is uncertain, mainly because information at the molecular level is limited. In an effort to understand the molecular basis of microtubule-based moveme nt, we isolated from tobacco pollen tubes polypeptides that cosediment with microtubules in an ATP-dependent manner. Major polypeptides released from microtubules by ATP (ATP-MAPs) had molecular masses of 90, 80, and 41 kD. S everal findings indicate that the 90-kD ATP-MAP is a kinesin-related motor: binding of the polypeptide to microtubules was enhanced by the nonhydrolyz able ATP analog AMP-PNP; the 90-kD polypeptide reacted specifically with a peptide antibody directed against a highly conserved region in the motor do main of the kinesin superfamily; purified 90-kD ATP-MAP induced microtubule s to glide in motility assays in vitro; and the 90-kD ATP-MAP cofractionate d with microtubule-activated ATPase activity. Immunolocalization studies in dicated that the 90-kD ATP-MAP binds to organelles associated with microtub ules in the cortical region of the pollen tube. These findings suggest that the 90-kD ATP-MAP is a kinesin-related microtubule motor that moves organe lles in the cortex of growing pollen tubes.