UNIDIRECTIONAL MOVEMENT OF FLUORESCENT MICROTUBULES ON ROWS OF DYNEINARMS OF DISINTEGRATED AXONEMES

Tetramethylrhodamine-labelled microtubules were observed to move on ro ws of dynein arms of sea urchin sperm axonemes exposed by elastase-ind uced sliding disintegration. The microtubules moved towards the flagel lar tip at a velocity of 3.1+/-2.1 mu m second(-1) (mean +/- s.d., n=5 3) in the presence of 0.1 mM ATP at 22 degrees C, but none moved towar ds the sperm head. We also examined the polarity of microtubule bindin g to axonemal doublet microtubules in the absence of ATP by using micr otubules brightly labelled at their minus-ends, In 140 of 210 microtub ules studied, they bound to axonemal microtubules with a parallel pola rity, These results suggest that tightly packed dynein arms on the out er doublet microtubules of sperm axoneme preferentially bind microtubu les to themselves with the same polarity as that of the axoneme and th at they generate a force to move only these microtubules in the direct ion away from the sperm head.