Microtubule-Stabilizing Activity of Microtubule-Associated Proteins (MAPs) Is Due to Increase in Frequency of Rescue in Dynamic Instability : Shortening Length Decreases with Binding of MAPs onto Microtubules

摘要: The role of microtubule associated proteins (MAPs) on the dynamic instability microtubules was examined under a dark-field microscope using bovine brain tubulin purified by DEAE-Sepharose column chromatography. In absence MAPs, transition from shortening phase to growing (the rescue) occurred rarely both in self-assembled and seeded ones, especially at plus end. Even conditions unfavorable stabilize microtubule, addition small amount crude MAPs or protein 2 allowed them undergo rescue. At increased concentrations MAP2, length change required for rescue during ("shortening length") catastrophe (transition phase) ("growth decreased. Under these conditions, often same site where previous rescues occurred. Distribution immunofluorescent MAP2 antibodies along individual showed that molecules bound onto forming discrete clusters. number per cluster estimated be between 25 60. Because "shortening length" distance clusters decreased with concentration, we suggest may form specific which readily stops. possibly regulates stopping shortening, is prerequisite