ANAPHASE CHROMATID MOTION - INVOLVEMENT OF TYPE-II DNA TOPOISOMERASES

Sister chromatids are topologically intertwined at the onset of anapha se: their segregation during anaphase is known to require strand-passi ng activity by type II DNA topoisomerase. We propose that the removal of the intertwinings involves at the same time the traction of the mit otic spindle and the activity of topoisomerases. This implies that the velocity of the chromatids is compatible with the kinetic constraints imposed by the enzymatic reaction. We show that the greatest observed velocities (about 0.1 mu m s(-1)) are close to the theoretical upper bound compatible with both the diffusion rate (calculated here within a probabilistic model) and the measured reaction rate of the enzyme.