Fig. 10. Model of microtubular oscillations. (1) The microtubules ahead of the nucleus depolymerise as they are pulled by Dhc1p, as proposed by Yamamoto et al. (Yamamoto et al., 2001). Ssm4p activates Dhc1p motor activity and ensures that the microtubules can interact with the cortical anchor, whose presence was proposed by Yamamoto et al. The microtubules behind the nucleus polymerise more slowly than the ones ahead are depolymerising and so they cannot reach the cell end and interact with the cortical anchor. (2) When the overlap region reaches the end of the cell, microtubules can no longer depolymerise and they dissociate from their cortical anchor, the putative dynein-dynactin complex, which is moving in the minus direction, is no longer anchored at the cortex and so could move towards the SPB. (3) When microtubules lose their cortical anchor they will no longer be pulled, the microtubules behind will be able to grow until they reach the cortical anchors in the opposite end. The anchors, or another factor at the cell ends, might induce microtubules to pause. Ssm4p will then accumulate at the microtubule tips, generating a stable interaction with the cortex and triggering microtubule depolymerisation. Dhc1p will also accumulate at the tips of microtubules, stabilised by Ssm4, which will also activate the motor activity of Dhc1p, which will start pulling the nucleus in the opposite direction. Alternatively, when the SPB reaches the cell end, it sends a signal to the opposite microtubule tip, activating it for an interaction with the cortical anchor.