MICROTUBULES: EVIDENCE FOR 13 PROTOFILAMENTS

TLDR

Microtubule subunit structure can be directly visualized by fixing in glutaraldehyde with tannic acid and cutting thin sections, eliminating the need for image reinforcement. The study presents a model of the microtubule. The authors examined seven microtubule types—including heliozoan axoneme, mitotic apparatus, contractile axostyle, chick brain repolymerized microtubules, flagellar central pair, and A tubules of flagella and basal body—to assess their subunit organization. All examined microtubules consist of 13 equally spaced protofilaments, while B tubules in flagella and basal bodies contain 11 subunits, and the inter‑protofilament connections between B–A and C–B are described.

Abstract

When microtubules are fixed in glutaraldehyde in the presence of tannic acid and thin sections cut, the subunit structure of the microtubule is readily observed without the need of image reinforcement. Seven types of microtubules were analyzed: those in the heliozoan axoneme, the mitotic apparatus, the contractile axostyle, repolymerized microtubules derived from the chick brain, the central pair in flagella, and the A tubules of flagella and the basal body. In all cases microtubules were composed of 13 equally spaced protofilaments. The B tubules in flagella and the basal body appear to be composed of 11 subunits. The connections of the B to the A and the C to the B are described. A model of a microtubule is presented.