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Science. 2019 Jan 18;363(6424):285-288. doi: 10.1126/science.aav2567.

Flagellar microtubule doublet assembly in vitro reveals a regulatory role of tubulin C-terminal tails.

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Department of Cell Biology, Sciences III, University of Geneva, Geneva, Switzerland.
Institute of Biotechnology of the Czech Academy of Sciences, BIOCEV, Vestec, Czech Republic.
Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czech Republic.
Institut Curie, PSL Research University, CNRS UMR 9187 - INSERM U1196, Paris-Saclay University, F-91405 Orsay, France.
Interdisciplinary Centre for Electron Microscopy, Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
Department of Cell Biology, Sciences III, University of Geneva, Geneva, Switzerland.


Microtubule doublets (MTDs), consisting of an incomplete B-microtubule at the surface of a complete A-microtubule, provide a structural scaffold mediating intraflagellar transport and ciliary beating. Despite the fundamental role of MTDs, the molecular mechanism governing their formation is unknown. We used a cell-free assay to demonstrate a crucial inhibitory role of the carboxyl-terminal (C-terminal) tail of tubulin in MTD assembly. Removal of the C-terminal tail of an assembled A-microtubule allowed for the nucleation of a B-microtubule on its surface. C-terminal tails of only one A-microtubule protofilament inhibited this side-to-surface tubulin interaction, which would be overcome in vivo with binding protein partners. The dynamics of B-microtubule nucleation and its distinctive isotropic elongation was elucidated by using live imaging. Thus, inherent interaction properties of tubulin provide a structural basis driving flagellar MTD assembly.


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