Microtubule dynamics in vitro are regulated by the tubulin isotype composition

Abstract

The growing and shortening dynamics of individual bovine brain microtubules at their plus ends at steady state in vitro, assembled from isotypically pure αβ_II, αβ_III, or αβ_IV tubulin dimers, were determined by differential interference contrast video microscopy. Microtubules assembled from the purified αβ_III isotype were considerably more dynamic than microtubules made from the αβ_II or αβ_IV isotypes or from unfractionated phosphocellulose-purified tubulin. Furthermore, increasing the proportion of the αβ_II isotype in a mixture of the αβ_II and αβ_III isotypes suppressed microtubule dynamics, demonstrating that microtubule dynamics can be influenced by the tubulin isotype composition. The data support the hypothesis that cells might determine the dynamic properties and functions of its microtubules in part by altering the relative amounts of the different tubulin isotypes.