Fig. 5. Possible functions of the MOR1 HEAT repeat-1 (HR1) in microtubule stabilization. (A) HR1 links microtubules to the plasma membrane via a plasma-membrane-associated protein. At restrictive temperature, this loss of binding dissociates microtubules from the plasma membrane, promoting their destabilization. (B) HR1 competes with a destabilizing protein (probably a kin1-like kinesin) for binding. At permissive temperature, the high affinity of MOR1 for this site prevents destabilization. At 29°C, this affinity is lost, leading to kin1-dependent destabilization and microtubule shortening.