Chapter 11 A Direct Method for Analyzing the Polymerization Kinetics at the Two Ends of a Microtubule

Abstract

Publisher Summary This chapter discusses the axoneme–subunit system in detail and describes three applications of the system that illustrate how it can be used for the study of microtubule polarity at the molecular level. Microtubules have an intrinsic structural polarity, which means that the two ends of a microtubule are physically and chemically distinct. This structural polarity is reflected in the polarity of microtubule growth. The axoneme–subunit system, although heterologous in nature, possesses two important advantages: It allows in vitro study of the polymerization properties of 13-protofilament microtubules and allows separate analyses of growth and depolymerization at the two ends. Another application of the axoneme–subunit system is its ability to test the polarity of drug–tubulin interaction. To illustrate this application, the effects of colchicine on growth and depolymerization of axoneme-nucleated microtubules have been tested. The axoneme–subunit system is a relatively simple technique that is well-suited for the in vitro study of several aspects of microtubule polarity. The main feature of this system is the direct visualization of changes in microtubule length that can be attributed to the sum of addition and loss of subunits at a defined end. There is an absolute identification of the two ends.